Fix infinite digest cycle caused by feature flag client

This was a fun bug. If multiple feature checks are done in rapid
succession when the features cache is empty (such as, for example,
during the first digest cycle at application boot time) then the
features client would keep kicking off HTTP requests until the first one
returned.

This would clearly be a misfeature, but wouldn't actually have caused
any problems but for the fact that the spinner in
`h/directives/simple-search.coffee` does this to determine whether to
spin:

    scope.$watch (-> $http.pendingRequests.length), (pending) ->
      scope.loading = (pending > 0)

This means that kicking off dozens of requests at a time keeps
invalidating the digest cycle (because the value of
`$http.pendingRequests.length` keeps changing), so it never ends. The
result is the ever-horrible `infdig` (infinite digest cycle) error from
Angular: https://docs.angularjs.org/error/$rootScope/infdig.

The angular $httpBackend mocking service supports two primary means of
usage:

   .expect(...).respond(...)

and

   .when(...).respond(...)

The latter pattern allows a single handler to respond to multiple
requests, in any order. The latter is precise -- one .expect() must be
matched by one request, in the correct order.

This commit changes the tests for the "features" service to use this
more precise form of testing.

PDF usages might want to specify relative URLs to get around proxy
restrictions with a custom viewer. Even link tags support relative
URLs for rel=canonical though it's probably a bad idea as a publisher.
In any case, we should clearly just do this.

Make Makefile more dumb

Add support for flagging user accounts as "not in public site areas"

Getting picky with our code styles

Added use strict.
Removed unused `attrs` var;

Docs URL line length is a bit too long...

The single it() in this test module was not being run (it was indented
inside a beforeEach()) and dedenting it reveals that the beforeEach() is
actually crashing anyway (controller somehow not registering with the
$controller service, looks like).

Rewrite the module to work and be clearer.

Stop two sources of dangling transactions

Add angular-csp.css

When on individual annotation pages like /a/<annotation_id> make an API
request to /api/annotations/<annotaion_id> instead of to the search API.
This bypasses the search API's NIPSA-filtering.

If you have a direct link to an annotations individual page, then you
can see the annotation (and all its replies) regardless of whether
anything is NIPSA'd or any user is logged-in.

Decaffeinate config/accounts.coffee & accounts/*.coffee

Add .jscrc for JavaScript Code Style help

JSCS is like JSHint, but specifically for Code Style.

It comes with a Google Code Style (which we use currently)
pre-set. This config file sets that and can be extended
later for any departures we make (if any) from that style
guide.

Replace pyramid_layout with basic template inheritance

Don't via via

Fixes #2371
Adds test.

Extract PDF anchoring closures

Search for one URI

Introduce the h.api.uri module for URI normalisation/expansion

Previously, when loading Hypothesis into a page, the client would make
one search request for each and every URI found on the page, including
those found by the document metadata scanners (in the Annotator
"Document" and "PDF" plugins.)

This is wasteful of network bandwidth, and moreover should not be
necessary in most cases due to the ability to expand to equivalent URIs
on the server side.

The component responsible for coordinating communication across page
frames is the "crossframe" service. This services maintains a registry
of page frames (previously called "providers") and their associated
metadata. This commit reduces the metadata stored to simply the page
URL, or in the case of PDF documents, the fingerprint URN.

It's worth noting that this *does* change behaviour in one important
way: if a page contains document equivalence data that we've never seen
before, and one of the alternate URIs has already been annotated, then
this change will mean we do not load annotations until that page itself
has been annotated (and thus the document equivalence data updated). I
am assuming that this is an extreme edge case.

Anchoring rewrite

s/viewable/visible/