Several refactoring tasks where made:
- Removed the old Widget::id field (JID).
- Renamed Widget::get/setName to get/setId.
- Moved load_widget_from_xmlfile() to app::load_widget and WidgetLoader
class.
- Removed jhook structure & jwidget_add_hook function. Hooks were replaced
subclassing widgets.
- Added InitThemeEvent class and Widget::onInitTheme member function.
+ 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.
