+ Added Filter, FilterManager, and FilterIndexedData interfaces.
+ Moved all widgets related to filters to src/commands/filters.
+ Added the filters library.
+ Added FilterWindow and one derived window for each filter.
+ Add ButtonBase::Click signal.
+ Button does not close the window by default (you have to configure this action manually when Click signal is triggered).
+ Add "closewindow" attribute to <button> widget in XML files.
+ Move "bevels" to SkinProperty.
+ Convert colorbutton widget in ColorButton C++ class.