Cloud merging: when sharing grammars between two devices that previously each
had separate grammar directoies on the server, clean up one of the directories
and make it a symbolic link to the other.
This lets the user access the same set of grammars from multiple devices.
Sharing grammars between multiple users is possible but discouraged at the
moment. There is no version handling, so concurrent editing of the same grammar
by different users might result in one user overwriting changes made by
another user. (The same goes for cuncurrent editing on multiple devices by
a single user, of course.)
