Fixed: scroll wheel speed is way to low in firefox

I increased scroll wheel speed to a sensible value
formatting
symbolic constant
Merge pull request #2013 from daboe01/fix-scrollwheel-speed-on-firefox

Fixed: scroll wheel speed is way to low in firefox [+1]
New: CPEvent scrollingDeltaX, scrollingDeltaY and hasPreciseScrollingDeltas.

Refs #2013.
New: support line-by-line scrolling with old scroll wheel devices in Firefox.

Without this change, using a traditional scroll wheel mouse with discrete steps would result in very slow scrolling in Firefox.

With this fix we handle these events like in Cocoa: as "[im]preciseScrollingDeltas", which `CPScrollView` in turn knows to apply the configurable line scroll amount for. For backwards compatibility, [event deltaX] and [event deltaY] are premultiplied with a suitable constant, while [event scrollingDeltaX] and [event scrollingDeltaY] show the true values needed.

Browsers other than Firefox seem to always send pixel scrolling information even for old style scrolling devices, at least on the Mac, so are not affected by this change.

Fixes #2013.