[applets/systemtray] Lazy initialize SystemTray model
Summary: SystemTray model was created in the constructor, delay initialization and create it lazily.
SystemTray::appletAdded signal is connected to both SystemTray's
Containment must be connected first, because it sets
some properties of newly added applet:
visible to false and
to the root item (container). If
Containment is connected second, then
newly created applet is added to the model and rendered, but immediately
Containment changes visibility to false.
- Do not play anything (no Medial Player icon at all)
- Run Gwenview
- Check if Medial Player icon in hidden view is rendered correct.
Before change: Sometimes icon is not rendered, looks like invisible or fully transparent.
After change: Icon rendered correctly.