Purely cosmetic cleanups to VinylControl / VinylControlXwax.

* Delete dead code.

* Initialize all variables.

* Clarify some variable names.

* Move member-variables to local when used purely as locals.

* Comment a lot of the member variables.
Remove dead code.
Rename remaining non-m_-prefixed variables.
Attack of the style police.
Refactor EngineBufferScale::getScaled API to be a little more clear.

* Get rid of the split between rate and tempo -- just represent it as speed.
* Split baserate out of rate.
* Add a boolean that indicates whether the speed affects the pitch or not.
Add a minimum seek speed to EngineBufferScaleRubberBand. Workaround for Bug #1263233.
Add a last-ditch effort workaround for Bug #1263233 in case our workaround in 1cbbf166 fails.
Oops, fix last-ditch workaround to work going backwards.
Get rid of log messages on resize. Fixes Bug #1263484.
Add support for 'ppc' and 'ppc64' as valid machine types.
Prevent some master sync party-stoppers:
* Deck passthrough activates -> sync disables
* Track ejected -> if master, sync disables, otherwise no change.
* Beatgrid on track cleared or becomes empty (0BPM) -> if quantize enabled, disable it (that's all we can do from bpmcontrol)
Prevent another party stopper
* If track is loaded or unloaded on explicit master, hand off.
Delete WAbstractControl.
Delete unused WSlider class.
Merge pull request #128 from ywwg/master_sync-party_stoppers

Prevent some master sync party-stoppers
Merge pull request #129 from rryan/vc_refactor

Purely cosmetic cleanups to VinylControl / VinylControlXwax.
Refactor WDisplay to use a QVector of pixmaps.
Make WKnob inherit from WDisplay.

WKnob shared a bunch of common logic with WDisplay since it's basically a
WDisplay with input. WDisplay now has support for backgrounds and "disabled"
widget support.
Get rid of manual reference counting in WPixmapStore and just use QSharedPointer.