Update "Projects > Open" menu when a data view is loaded
Update "Projects > Open" menu when a data view is loaded

When normal data views were loaded, the "Open" submenu within the
"Projects" menu, wouldn't have any content. This commit fixes this and
triggers an update of the menu when a data view is loaded.  Fixes #535.

htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID,htem/CATMAID,htem/CATMAID,fzadow/CATMAID