shared: Allow for multiple user type dbs
shared: Allow for multiple user type dbs

Previously all user type dbs were hardcoded to be of name user-<uid>
making any additional user dbs ignored by buxton even if the dbs were
specified in the configuration file.

Change this by using the same convention as system dbs, using the
layer_name-<uid> convention of db file name.

sofar/buxton,sofar/buxton