Merge pull request #10 from solros/master

minor modifications
moved query to DatabaseAccess
implemented table view, no selection or update yet
rearranged database window
added constraints
check for extension poly_db, otherwise deactivate database menu
detect missing internet connection or db time out during database and collection query
more error handling
basic error handling if loading from database fails
clear list of IDs if collection changes
Merge remote-tracking branch 'upstream/master'