fix indexes in getItemAt and createContextMenu
make snatch visible by public
added smooth scroll support
improve start scroll by events
additional checks in start scroll
Merge branch 'fire-master'

Conflicts:
	library/src/main/java/com/etsy/android/grid/ExtendableListView.java
	library/src/main/java/com/etsy/android/grid/StaggeredGridView.java