When a launcher plugin is removed, it tries to cleanup
the desktop dir. Hower this might fail because of leftover
files in the (re-used) directory from a previously
craches launcher.

Only print this in the terminal, because nothing is going
'wrong', just not so nice.

Add a quick signal back to the code and improve the internal
handling so the objects are better isolated.

Bug #5707.

With this function a plugin can remove itself from the panel
without user intervention.

Same implementation as old panel, but this time in
a loop to drop a lot of duplicated code.

Some styles properties for the minimized icon lucency,
max width chars and ellipsize mode, that were previously
hard-coded in the source.

The restart counter was a bit flawed, because if the panel would
run for weeks and 3 restarts occured, it's not a big deal, still
the panel would've bothered the user what to do.

We now use a minimum time between restarts, if there was another
restart in the last 60 seconds, ask the user what to do.

You can now quickly enable or disable the tooltips with the
following command:

xfce4-panel --plugin-event=launcher:disable-tooltips:bool:true