Clarify supported platforms for `elevation` property
Clarify supported platforms for `elevation` property

The docs previous did not make clear that the elevation is supported on
iOS and Android (starting from Android 5).

Change-Id: I1010a124c4049e7e8ee638d3a0b9a149344a833c

eclipsesource/tabris-js,eclipsesource/tabris-js,eclipsesource/tabris-js