With this change we have moved all the file selector customization to
a new special FileExportWindow. So the file selector is used only to
select the output file (no more FileSelectorDelegate = now we can use
the native file selector for File > Export).
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.
