git-lfs lock/unlock

It would be great if TortoiseGit supported git-lfs locking functionality. This allows files to be locked so that other team members can not modify them at the same time. This is useful for, e.g. binary files, images, or other non-mergeable files.

The interface is simple. git lfs lock <filename> locks a file git lfs unlock <filename> unlocks the file again. git lfs locks gives a list of files currently locked, and the users who have locked them. Files which have not been locked by the user are automatically set as read-only, and will cause a push to fail (or at least give a message if the server is not configured to support git-lfs locking).

My proposal would be to add "Lock" and "Unlock" context menu options for files, as well as a "Lock list" menu option which would bring up a window similar to e.g. the "Check for modifications" option which would list all currently locked files. It would also be nice if locked files had a unique icon.

Related to #2972