* ui lua integration: streamline of api

* abstractscrollbar, abstractscrollable both have direct methods to manipulate
* the scroll pos/size
* abstractoption allowed manipulation only through the scrollY field
* this creates a lot of confusion so i moved the manipulation methods
* up to the level op abstractoption, bringing this class api in line
* with other similar classes

* of course, one might wonder why we need so many abstract base classes
* having similar methods...