Flickable: Use increased default flick parameters on BB10

Due to the high resolution the display default flicking speed
is rather slow. This change introduces increased values of
QML_FLICK_DEFAULTMAXVELOCITY and QML_FLICK_DEFAULTDECELERATION
which feel closer to the native experience.

Also cleans up the flick variables a little by moving them to
their own header, so that QQuickPathView can also benefit from
the improved behavior on BB10.

Change-Id: I80878d4cc2a53a8f530b1dc8674f729f70a83119
Reviewed-by: Alan Alpert <aalpert@blackberry.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>