Make sparkle color and alpha customizable

This CL introduces a new attr: effectColor.
The attribute can be used on ripple tags to customize the color and
alpha of the ripple decoration.

It's also possible to change the effect color via code by invoking
RippleDrawable#setEffectColor.

Fixes: 185602477
Test: atest RippleDrawableTest
Change-Id: I9b50f330729a67ef4b529283a92c83c28387fa0b