Move the user's current email address out of the placeholder attribute
of the new email address <input> field. Just put it in a <p> instead.
This is much better for usability.

Quite a lot of repetition in these tests, some shared helper functions needed.

Begin adding frontend tests for the new AccountController code that
deals with the new form for changing the logged-in user's email address.

I've done this as a new top-level describe() with a new way of writing
Angular controller tests, rather than adding to the stuff already in
account-controller-test.coffee.

The aims of this way of writing tests is to make the tests easier to understand
and modify (either to fix a broken test or to add new ones) by:

- Reducing special Angular knowledge needed to understand the tests

- Reducing globals (both global variables and beforeEach() functions) used in
  tests.

  These increase the "travel" needed to understand a given test method because
  you have to read the whole test module to understand everything that happens
  before the test runs and what all the global variables the test uses are.

  The aim is that reading only the test function (and not the rest of the code
  in the file) should be enough to understand the test.

  Similarly I shouldn't have to read and understand the whole test file to add
  a new test.

  Globals and beforeEach()'s also tie the tests together. For example if a
  bunch of stub services and a controller are created in beforeEach() functions
  then any new tests added to the file inherit this stubbing behaviour even
  though they may not want it or may need something else. This again makes
  changing or adding just one test harder - need to understand the whole file,
  changes made for one test may break other tests.

Implementation notes:

- Used a new top-level describe(), didn't want to inherit all the globals,
  beforeEach()'s and stubbing of the existing one.

- Because we now have two top-level describe()s had to use a try ... catch in
  the second one to avoid creating the "h" Angular module twice.

- Tried to decouple the tests from Angular as much as possible, reduce the
  amount of Angular knowledge (especially about providing and injecting
  dependencies) needed to understand the tests.

  Angular's $provide isn't used at all, and inject() (which I don't think can
  be removed completely) is contained in two helper functions.

- Rather than a beforeEach() and global variables we use a controller()
  function that creates the AccountController and stubs for the services it
  depends on and returns an object of all of them.

  Tests can then call controller() and use destructuring assignment to get only
  the bits they need.

  Every variable used in a test method is defined in the test method
  (sometimes by calling a helper function and getting a return value).

- controller() by default uses minimal stubbing, but the caller can optionally
  pass in their own object for each of the stubbed dependencies.

Fixes #174.

account.html:

- Add a new "Change Your Email Address" form

accounts/views.py:

- Add email to the user dict returned at /app?__formid__=profile (or
  session.profile() in Angular)

- When resetting the form after a successful submission, put the new (or
  unchanged) email address into the user dict returned in the response.
  AccountController needs this (see below).

account-controller.coffee:

- Add $scope.email (the user's current email address), to use for placeholder
  text in the email form field.

- After a successful form submission set $scope.email to the one from the
  response. This sets the placeholder text in the email field to the new value,
  instead of continuing to show the old email address as placeholder.

- Add changeEmail() method to receive email form submissions.

Display KaTeX parse error upon faliure to parse

Added mathjax fallback to inline rendering

Add URL params to /stream.atom

This reverts commit f6787df785c8c8e2bdbf4d7b65a9176adad64d19, reversing
changes made to 29d975367171b8d4e69941c3f0e5d40ddfc98ddc.

I'm afraid I've had to revert this:

- it introduced a crashing bug on master (see
  https://github.com/hypothesis/h/pull/2131#discussion_r30692024)
- feature flags are no longer accessible by view functions (the
  configurator object is not available from the request), thus this
  blocks #2131

Prospector tweaks

Make our Prospector settings much stricter

Features cleanup

Snap the sidebar closed as well as open

Merge pull request #2197 from hypothesis/1142-no-client-side-error-message-when-saving-annotation-fails

Add a client-side error when saving an annotation fails

Close #2162

Change annotation card action from 'share' to 'link'

When creating a new annotation, on the front-end, if the server fails
when trying to save the annotation, then:

1. Show an error message to the user
2. Don't close the annotation editor

Hide the widget panel until ready for input

Updated text, tooltip, and icon for the link to the standalone page.

Close #2097

I'm not sure where I got the number that was here, but it's not the
well-known maximum value for any browser.

Since our div is likely to be one of the last in the document, by
virtue of being dynamically injected after DOMReady, close #1909.

Close #2207