MyCyma

[fix] display a proper error page when an object is not found

[evol] added set view and linked it from tree view

[fix] sets should be ordered in tree view

[evol] created display_artwork_frame() helper function and now use it in the welcome page + created a set/group tree view with it too

[fix] wrong method call

[evol] use SQL sessions instead of cookies-based ones

[evol] added image size info in the 'latest 10 artworks' page (closes #7)

[evol] added a small margin around image in the 'latest 10 artworks' page

[fix] corrected language display in user view

[evol] language can be forced in the user admin page (closes #6) (no user interface yet)