cleanup
bugfix: do not hide the table if settings are wrong (see below)

wrong settings: until now the user was able to resize the columns when the gallery was active!
therefore every column (should have been) was invisible and that's what was stored as settings.
settings = every column hidden = no way to display the table again...
fix: 1. do not save hide-every-column-settings. 2. display the default settings if everything was insvisible
bugfix: ignore "hide everything" settings when saving
datatable: prevent 403 errors for not authenticated users

access callback => usre_is_logged_in produces 403 errors for each flexigrid reload, resize oder column change...