Theme refactoring.
* transparently load the common CSS file of the current theme. widgets don't have anymore to explicitly ask the loader to load common theme CSS definitions.
* removes common_template
* updates deliteful widget to use the new structure
* allow widgets to use thier own variables.less to share variable between rtl/ltr less file without generating css.js file.
* remove mobile and d-background classes
Added tests for ViewStack/LinearLayout/Scrollable styling issues
make it work
More test cases, this time without using List or ScrollableContainer