GNOME 3.14

Original PR #5052 

Problems:
- We use NM 0.9.10.0 only in GNOME 3.14 for now, until a bug which shows vbox interface in the UI is fixed.
- Since GNOME 3.12 does not work well with GTK+ 3.14, we use GTK+ 3.14 only for GNOME 3.14. This means a lot of rebuilds because of the two gtk (and two webkit). I will drop GNOME 3.12 as soon as possible.