This commit allows themes and theme components to have QUnit tests. To add tests to your theme/component, create a top-level directory in your theme and name it `test`, and Discourse will save all the files in that directory (and its sub-directories) as "tests files" in the database. While tests files/directories are not required to be organized in a specific way, we recommend that you follow Discourse core's tests [structure](https://github.com/discourse/discourse/tree/master/app/assets/javascripts/discourse/tests).
Writing theme tests should be identical to writing plugins or core tests; all the `import` statements and APIs that you see in core (or plugins) to define/setup tests should just work in themes.
You do need a working Discourse install to run theme tests, and you have 2 ways to run theme tests:
* In the browser at the `/qunit` route. `/qunit` will run tests of all active themes/components as well as core and plugins. The `/qunit` now accepts a `theme_name` or `theme_url` params that you can use to run tests of a specific theme/component like so: `/qunit?theme_name=<your_theme_name>`.
* In the command line using the `themes:qunit` rake task. This take is meant to run tests of a single theme/component so you need to provide it with a theme name or URL like so: `bundle exec rake themes:qunit[name=<theme_name>]` or `bundle exec rake themes:qunit[url=<theme_url>]`.
There are some refactors to internal code that's responsible for processing themes/components in Discourse, most notably:
* `<script type="text/discourse-plugin">` tags are automatically converted to modules.
* The `theme-settings` service is removed in favor of a simple `lib` file responsible for managing theme settings. This was done to allow us to register/lookup theme settings very early in our Ember app lifecycle and because there was no reason for it to be an Ember service.
These refactors should 100% backward compatible and invisible to theme developers.
* Introduced fab!, a helper that creates database state for a group
It's almost identical to let_it_be, except:
1. It creates a new object for each test by default,
2. You can disable it using PREFABRICATION=0
Attempt to force NGINX to include content length when doing X-SendFile
This does not seem to be required when bypassing NGINX.
Without this header some CDNs may have issues caching
