PSculpt: Port over Scrollwheel / +/- event support while sculpting, for changing brush strength + size

* WheelUp/+ = Increase
* WheelDown/- = Decrease

* With Shift = Strength
* Without = Size

PSculpt: Rate/Timer support

* Twist and Reset also support the rate control now
* Reduced the speed of the timer, to make it more controllable

PSculpt: Code Cleanup - Remove some old debugging cruft

PSculpt: Code Cleanup - Unify the "pso vs data" divide

PSculpt: Make pressure and falloff configurable options, as in other sculpt brush systems

PSculpt: Code Cleanup - Move the header prints to a separate function

PSculpt: Show help text showing key methods of operation in the header

PSculpt: "Invert Mode" for "Reset" brush

Now, when holding the shift key when using the Reset brush, the tool will
blend the pose back towards the state the pose was in before the start of
the sculpt operation. The idea here is that this makes it easier to revert
errors (such as accidentally overshooting on where you'd intended to revert
back to)

PSculpt: Bugfix - "invert" doesn't get unset if shiftkey is released

PSculpt: Store original unaffected values in tAffectedBone

PSculpt: Code Cleanup - Unify all the *data's, and stop passing it around everywhere

PSculpt: Pressure and Influence Cleanups

* Use tablet pressure to control strength of effect. More work is still needed
to be able to turn this on and off as needed (i.e. the little toggle for pressure
sensitivity)

* Currently, all places which use this now use linear falloff. This again should
be controllable by the user.

* TODO: Discovered a bug with how the "data" structs are getting used. It turns out
that the pso->data is not getting used, while a separate "clean slate" is getting
created each time.

PSculpt: Autokeying Support

When autokeying is enabled, bones will automatically be keyed using the
"Whole Character" Keying Set.

TODO:
* Add support for only doing partial keying - perhaps by having options
for controlling what gets used to do this?

Code Cleanup - In preparation for some OpenGL drawing cleanups in master

PSculpt: Hacky first attempt at "superbrush" mode for Adjust

Instead of inverting the brush behaviour, holding shift for the Adjust brush
will instead activate grab, making it easier to switch between these without
having to go via the buttons.

Verdict:
This only works partially. It still doesn't feel right - especially with the
Sintel rig, as the arm FK rotations feel like they go in the wrong directions.

PSculpt: Code Cleanup - Split logic for trackball calculations into a separate callback

PSculpt: Assorted Code Cleanups

* Reshuffled callbacks
* Fixed comments
* Made dvec be stored in the data stuff

PSculpt: Code Cleanup

* Improved naming of brush callbacks
* Removed redundant/unneeded vars

PSculpt: Code Cleanup - Remove some unneeded operations + type conversions

PSculpt: Rename Draw/Trackball -> Adjust

After a few days of playing around with this, it seems that, while close to the
behaviour we want, "trackball" doesn't quite act as a general purpose "Draw"
(i.e. you'd expect to be able to do line of action stuff with that, and trackball
fails for that case). However, trackball excels at another situation: tweaking
and adjusting existing poses to add a bit more character, or to generally improve the
pose "in place". Hence the decision to retain and rename this brush.

Notes:
* For now, "Draw" still does the same thing as Adjust. It'll stay that way until
I come up with a better draw brush
* Knocked out "Radial" and "Wrap" from the types enum for now. They'll come back
later when we actually implement them. Until then, they'll stay hidden, in case
we just want to knock them out completely (and to avoid confusing testers)