New account.upload_video (both local and remote)

It is now possible for accounts to upload videos using the resumable
upload protocol.

This commit does not implement the entire protocol, just the simple
case where the upload "goes through" in one step. Still to be implemented
are the cases in which the upload is actually resumed.
Merge pull request #19 from Fullscreen/upload-video

New account.upload_video (both local and remote)