Don't use forceActiveFocus to focus the applet toolbar

Generally, using forceActiveFocus is a bad thing since it indicates
something is wrong in how focus is setup. It is also unnecessary here.
PlasmoidHeading is a focus scope which means we can set whatever default
focus we want inside it and then simply focus the heading to get our
desired behaviour.

In addition, we now use Plasmoid.expanded to retrigger the focus binding
so that it is properly reset on re-showing the applet.