Do not activate containment when one of its applet is activated
This will also allow to delete the hack over plasma-desktop side of things.
Reasoning is that some applets use "activated" when they would to trigger their action, e.g. the show desktop applet. If the containment (here, the panel) also gets activated as a result, it will get mouse input and a blue line will appear. Previously this was avoided by some hacky code that (a) apparently was not working for some people and (b) broke auto-hide and dodge windows after clicking on "Minimize all".
Should be tested carefully! E.g. whether the panel appears when a window / applet requests attention.
Edited by Niccolò Venerandi