bluez: Add a Bluetooth Phonebook Access Profile backend using BlueZ 5

This pulls contacts out of a paired Bluetooth device and dumps them in
folks.

No test cases are included.

https://bugzilla.gnome.org/show_bug.cgi?id=685848

This bumps the Vala and GLib dependencies of folks, needed for the following
two fixes.
 • https://bugzilla.gnome.org/show_bug.cgi?id=710643
 • https://bugzilla.gnome.org/show_bug.cgi?id=710726

https://bugzilla.gnome.org/show_bug.cgi?id=685848