Add a move feature to DocumentsUI.

Add a menu item (protected behind a system property) for moving files.
Add an extra to the copy intent for transfer mode (copy/move).
Add code to CopyService to delete files after copy when in move mode.
Add tests.

BUG=20559838

Change-Id: I983f57a528327d1e7a12982b599094aad2c856ed
10 files changed