FileProvider Modal UI for uploads

Review Request #7009 — Created March 6, 2015 and updated — Latest diff uploaded

Review Board
reviewboard, students

In order to upload files with the FileProvider framework, a UI must be implemented to allow the user to interact with their file provider account. When a user selects Add File to upload a file, they will be presented with a modal with tabs to switch between two different types of upload: from local machine, from file provider. Uploading from local machine is the same old default upload mechanism.

When selecting upload from file provider, they would be presented with a new window to interact with their file provider. Things they can do are:
- switch between different accounts
- select a file to upload by clicking on it
- navigate through directories by double clicking them
- click on file/directory to display metadata for it on the side
- search for items in the file provider

There's also the caption and attachment history field as well, to match the current mechanism.

Manual testing of the UI and debugging to verify files.