SkinTheme: paint windows using styles
Replace jwidget_get_text_length/height with Widget::getTextWidth/Height

Renamed Widget::getTextSize to Widget::getTextLength as now getTextSize
returns a gfx::Size() (not the strlen() of the text)
"Put alpha" ink behaves as default ink in indexed mode
Fix ReplaceInkProcessing for indexed mode when opacity=255
Fix compilation warning in cmd_remove_layer.cpp
Fix issue 353: don't show context bar when a new view is activated

Now we have three modes: normal mode (everything is visible), the first
intermediate mode (context bar+sprite editor+timeline), and advanced mode
(sprite editor only).