Respect Accept-Language when getting strings

Update Transifex project name

allow pagination of responses within thread views

JIRA: FOR-374

Make retrieving user's active threads faster

The user profile page in the LMS only displays the thread title and
body, not comments, so do not bother returning them.

set up transifex

use yajl for json serialization

Set up Travis CI

Add tests for non-ASCII characters in comments

Due to a bug[1] in ActiveRecord's JSON serialization, tests for characters
outside the BMP are marked as pending.

[1]: https://github.com/rails/rails/issues/3727

set up i18n in comments service

* add i18n gem
* configure default_locale (en-US)
* externalize strings
* configure locale fallbacks
* add tests

Fail fast when database is unreachable

use rack-timeout 0.1.0beta3

fix syntax problem in unicorn config

disconnect default mongoid session after forking.

adjust new relic method tracing.

Fix Content-Type header

The default Content-Type is text/html, but all of our endpoints return
JSON, so Content-Type is now correctly set to application/json.

(also provide a switch for query-level debugging output from moped.)

optimize request timeout settings for heroku

* use Rack::Timeout, set to 20s
* set unicorn timeout to 25s

Ideally these are set lower, around 10s/15s, however we need to reduce long-running requests (such as notifier batch pulls) before we can safely do this.

Allow more endpoints to use commentable_ids param

The commentable_ids param is a comma-delimited list of ids indicating
that only threads belonging to one of the specified commentables should
be returned. It can now be used by any endpoint that delegates to
handle_threads_query (most importantly "#{APIPREFIX}/threads"), and
the commentable_id field is now indexed for efficient filtering. The
motivation for this change is to allow clients that are filtering by
commentable_ids to avoid using the /search/threads endpoint, which does
not do sorting and pagination correctly.