loading overlay : delay

* Pageloader, delay before page render
*pagetreeview, overlay during compute
*pagetreeview : expand first widget #250
Merge branch 'master' of github.com:Heigvd/Wegas

# By Francois-Xavier Aeberhard
# Via Francois-Xavier Aeberhard
* 'master' of github.com:Heigvd/Wegas:
  Fix #271
  Fix #282 Put activate everywhere
  Fix #232
  Fix #248