Blender Git Loki

Tweaks to New Driver creation behaviour

* 'Show Debug' now enabled for all newly created drivers. For most users, it is
useful to be able to see this to help figure out what's going on

* Removed failed experiment of creating new drivers with Generator FModifiers. I
had hoped that this would make it easier to create drivers that doubled or
halved the input values, but that has proved to not be the case, and instead
made harder for most users to set things up (as they'd have to remove these
first).

Now, when adding drivers from the UI, these get created with two keyframes (at
(0,0) and (1,1) for a 1-1 mapping), which can be easily tweaked normally.

However, for backwards compatability of scripts (notably rigify, and perhaps
some others out there), when creating drivers from scripts, they will still get
created with Generator FModifiers for now. We can review this situation again
for 2.7, but for now it seems ok.