lockscreen: Don't duplicate statusbar and action panel from shell

Currently we have two instances of the status bar, one in the shell and one on the lockscreen, since there isn't a way to show windows above the lockscreen.

With kwin!2385 (merged), there will be a way to do so.

We will need to dynamically turn on restricted mode when logged in, and somehow integrate with the lockscreen without being of the same QML application (ex. request unlock for action). We also need to ensure this is above any other windows raised above the lockscreen.