Our decoration is deleted using deleteLater() and that might cause access
to the bridge. Given that we also need to deleteLater() the
PreviewBridge.
To do so the PreviewBridge is no longer directly exposed to QML, but
in a wrapper object which holds the bridge as only element.
BUG: 344278
FIXED-IN: 5.4.3
REVIEW: 125724
The decoration button configuration interface is merged into the QML
part using two list views (left buttons, right buttons) and a grid
view for all the available buttons.
Following features are supported:
* finds all plugins
** finds all themes for a theme-engine plugin
* renders previews for the plugin/themes
* loads currently used plugin/theme
* saves selected plugin/theme
* triggers config reload in KWin
Following features are currently not supported:
* Search
* Plugin configuration
* GHNS
* Button configuration
