Manage ManuallyLockedException and disable editing on the buffer if file is locked.

[ArtificialOwl]

The FilesLock App returns OCP\Lock\ManuallyLockedException which extends LockedException when the file is locked and someone else tries to update or delete the file.

The ManuallyLockedException contains the owner of the lock and (should also returns) the time until the unlock.

The idea we talked about was to do some test on the file on opening to disable any edit on the buffer because, right now, any edit on the buffer made by the non-owner will be shared and saved by the owner of the file himself.

https://github.com/nextcloud/files_lock/blob/master/lib/Storage/LockWrapper.php#L94-L98

[juliusknorr]

This is handled now with #2248