* Created Snakbar class to encapsulate Snackbar logic.
* Clicking the action now emits event to current screen
* Action color works

Slightly more backwards compatibility in android leftButtons

When more then one modal was displayed, and dismissAllModals
was called, the top most modal was dismissed until no modals
were visible. This resulted in quirky animation since user saw
all modals getting dismissed.
This commit simply changes to order in which modals are dismissed to
avoid this bug.

This commit closes #224 and fixes #252. Calling `setButtons` with
`leftButton` object still works for now but is deprecated and will be
removed in future version.

This reverts commit d3582d2780.

fixes #253

This commit adds support for displaying an activity with no animation
by setting `animationType: none` when calling `startApp`. In the future
we can support more animation types if there's a demand for it.