This PR adds the first use of Uppy in our codebase, hidden behind a enable_experimental_image_uploader site setting. When the setting is enabled only the user card background uploader will use the new uppy-image-uploader component added in this PR.
I've introduced an UppyUpload mixin that has feature parity with the existing Upload mixin, and improves it slightly to deal with multiple/single file distinctions and validations better. For now, this just supports the XHRUpload plugin for uppy, which keeps our existing POST to /uploads.json.
* DEV: Use custom tags rather than handlebars server side
These will be skipped if they are ever rendered in a document. The
handlebars really messes stuff up.
* DEV: Build our own locale file for testing purposes
We can't practically proxy everything in test mode, but we can
approximate the logic and build our own locale file for testing purposes
that works quite well. This allows us to run tests without a proxy.
* DEV: Support for testem runner for ember cli tests
* DEV: Use Ember CLI middleware to decorate the index template
Previously we'd do this on the client side which did not support our
full plugin API. Now requests for the index template will contact the
dev server for a bootstrap.json and apply it to the current template.
* FIX: Allows logins in development mode for Ember CLI
