Fixed error causing examples not to run.
Removed "on_update" event and fps counter from examples.
Fixed error on call of TextureGraphicElementTemplate in Theme.
Added test case for Theme initialization and generation.
Renamed private attribute of Frame element in Theme.
Removed unnecessary function call.
Simplified reset_size to avoid multiple calls of layout in the tree.
Simplified manager's reset_size to avoid double call of layout.
Removed unnecessary reset_size of Wrapper.
Refactor of Viewer's reset_size to simpler terms.
Improved docs for viewer's reset_size.