Fixed delete action to show error message as notification
Removing trailing dot in path that samba doesn't seem to like

Fixes #5778
Added unit test for getId() and constructUrl()
Fixed SMB file deletion success detection

Since unlink() smb4php doesn't return true on deletion success, we need
to check whether the file was deleted to confirm success.

Fixes #5866
Merge pull request #5878 from owncloud/extstorage-smb

[SMB] Fix stat and unlink