MyCyma

[evol] added group view and linked it from the tree and set views

[fix] ensure link to the tree view in the menu works even if coming from a page in another namespace

[evol] artwork frame improvements #1

[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)