Implement RTL support in framework ViewPager, DatePicker

Lays out ViewPager in the opposite direction when in RTL mode, e.g.
the first item's starting edge is laid out at the largest possible
scrolling distance. This preserves both the meaning of positive
scrollX values and the meaning of positive adapter positions.

Also removes clickable attribute from DayPickerView since it has a
virtual view hierarchy.

Bug: 19408740
Bug: 20134073
Change-Id: Ib6f945335bd88da59c8c593c7c270e290e15d0a5