Backbone view for attachment upload

Review Request #5911 — Created May 31, 2014 and submitted — Latest diff uploaded

Review Board
reviewboard, students

A working version of a Backbone view for file uploads (the one that you see when you click Update -> Add File). Previously that popup is used gReviewRequest hack. Now it's a standalone view, as that view is also needed for attachment revisioning.

Side note: The only other thing that needs gReviewRequest hack is "Update Diff" popup. Once someone writes a view for that, gReviewRequest can be removed.

Tested: * Uploading new attachments. * Error when no attachment is specified. * Multiple errors returned from server side (see screenshots).