* Use header (with integrated buttons when shown as part of the system tray
Plasmoid)
* Use less space so it fits into the system tray plasmoid (at least on a
full HD screen with 96 dpi)
* Show action for internal errors only if there are internal errors (like
in the Qt Widgets based GUI)
* Port away from deprecated tab bar (which is not used in official
Plasmoids anymore as well)
* Simplify code for ensuring the minimum size as configured (still does
not work within the system tray Plasmoid)
Apparently just setting HOME does not work anymore. At least in my Plasma
setup XDG_DATA_HOME and XDG_CONFIG_HOME are now interfering. This change
introduced an extra helper script to take care of the environment variables
which unsets the XDG_… variables and also takes care of QT_PLUGIN_PATH by
the way.