Blender Git Loki

Drivers Setup: Expose all mapping types for creating drivers

* This includes the "manually create" modes, which correspond to the previous behaviour
for setting up drivers. This is necessary when the current screen layout is not
well suited to having multiple property editors open (e.g. small screen or heavily
subdivided screen).

* Only the modes relevant for the current property type (i.e. array vs single)
will be shown

* The "Add Driver" entries in the RMB context menu have now been replaced by a
submenu which will list all the available mapping types.

* NOTE: The code for the ANIM_OT_button_driver_add() operator is perhaps a bit hairy.
However, it currently allows us to have the desired behaviour. It can always get
cleaned up later though.