refactored some constants so that they can be modified by the user.
refactored out the rounding of :attr:`DampedScrollEffect.value` when
coasting to stop to a new bool :attr:`round_value`.

But why does it need to be rounded in the first place?
Merge branch 'master' of https://github.com/kivy/kivy into refactor_kinetic
Merge pull request #1463 from eulerreich/refactor_kinetic

Refactor kinetic constants