Allowing the editing of remote themes has been something Discourse has advised against for some time. This commit removes the ability to edit or upload files to remote themes from Admin > Customize to enforce the recommended practice.
We were trying to observe a non-ember object which is undefined
behavior and was leaking to odd bugs. This replaces the `filter` object
with an Ember Object and things seem to work.
David Taylor
Roman Rizzi
Justin DiRose
Robin Ward