fix(avatars): disable remote URL option
fix(avatars): integrate profile server backend for profile images
fix(errors): use the correct context for error messages

Fixes #1660.

This issue occurred because the context of an error was being discarded as the error was rethrown in the form submission handler. Rather than depend on error context being passed around, we store it on individual error objects.
Pre-merge cleanup

* remove unused deps from base.js.
* remove `errors` parameter in `displayError` calls in views/mixins/service-mixin
Merge pull request #1584 from mozilla/profile-images-backend

fix(avatars): integrate the profile images backend

I give this my r+.