Add an ESLint rule to require this and fix up non-conforming code using
ESLint's --fix tool.

Refactor the streamer into a stand alone class

The group invite icon is only used in the H web service

* The corejs polyfills are not needed in the Gulpfile since we switched
   to a more recent version of Node

 * The Object.assign() polyfill does not need to be included in 'raven'
   or 'settings' because it is already included by the polyfills.js
   script

This was left over from when the Hypothesis client was extracted out
from the hypothesis/h repository, where the extension code currently
remains.

Enforce that all paths through a function either return a value
or do not return a value.

This cause several cases of spurious returns left in by CoffeeScript ->
JS conversion and return statements with missing values.

Fix 'time' tests in timezones behind UTC

Several test fixtures have expectations that the "current date", where
"current" is reset to the Unix epoch at the start of the tests, is 1st
Jan 1970. This is true in timezones equal to or ahead of UTC but not the
case for timezones behind UTC.

Resolve the issue by just advancing the fake clock forwards to midnight
on 01/01/1970 if the timezone is behind UTC at the start of the tests.

Annotation / Notes tabs copy update and style tweaks

Update UI state after search API request completes with no results

Remove sticky tab bar behavior

When a search API request returns results, the returned annotations are
added to the app state and this transition triggers a digest cycle.

When there are no results however, this was not happening and the value
of the 'isLoading()' function changed but no digest cycle was triggered
to pick this up and reflect it in the UI.

Since SearchClient's 'end' event is emitted asynchronously via a Promise
callback, $scope.$apply() or $evalAsync() must be used to ensure that
change detection runs.

The real solution will be to store all the information required to
determine the loading/not-loading state in the Redux store, so that any
transition automatically triggers a digest cycle. This requires some
more extensive refactoring however.

The sticky tab bar behavior has some UI issues that need to be resolved
before we could ship it. For example, when switching between tabs the
scroll position needs to be reset to the top.

For the time being, this commit removes the behavior.

Following feedback and design review, change the label from 'Notes' to
'Page Notes' to better distinguish notes from annotations and make the
empty state text for the Annotations tab more helpful by explaining to
users how to create a new annotation.

Shift the 'No annotations in this group' message down slightly to
prevent the border from being clipped.

Also prevent text selection in the tabs.

ESLint - Enable 'Best practices' rules

Usage of Hound has been replaced by a Travis task that runs `npm run
lint`

Enable additional rules from the 'Best Practices' list on ESLint's Rules
page.

Use `.delete` instead of `['delete']` etc. since all browsers we target
support ES5.

Add ESLint configuration and use it to replace JSCS / JSHint

These have been replaced by ESLint

For stylistic consistency, require semicolons rather than relying on
ASI.

Checking for return values in Array callbacks found several incorrect
uses of Array.map() where Array.forEach() should have been used.

This will aid migration to let/const in future

This will ease migration to let/const in future.

 - Remove unused variables. Note that ESLint is smarter than JSHint in
   that it realizes that vars which are assigned but never read are
   unused.

 - Add missing `angular` require statements.

 - Add ESLint suppressions where necessary

Add a basic ESLint configuration which uses ESLint' recommended
settings to check for basic errors such as undefined vars and unused
variables.

Improve tab bar input handling and accessibility

Use anchor rather than link elements for the tab bar items so that they
are focusable via keyboard navigation.

Also follow code conventions and use 'is-<state>' for element states set in JS.

Focus the Annotation and Notes tabs on touch or mouse down rather than
click.

This makes the tabs act more like tabs in native apps and feel more
responsive.

Since Angular does not provide a built-in attribute directive for
handling touch events, implement a custom one.