[AT-SPI] Move setting highlightability property for controls to inheriting classes

* Giving highlightable state explicitly for particular control by its developer is more reasonable than giving this state for all controls by default.
* Such approach allows for better control over UI elements highlightability. We avoid highlighting containers like layouts, etc.

Change-Id: Ifc1b5e268c2bd02c17498d0dba619771c5d5b00d