RFC: Put notifications in sidepanel like widget explorer

[kainz.a]

The thing I say hidden panel was that first we have widgets and panels
and in an widget you can only have one item in an panel you can move
different widgets and in my mind the user can say I want to see the
notifications, the weather and some configuration in this "sidepanel"

maybe you all know the wonderful what-if stories from kven
(https://kver.wordpress.com/2014/10/25/what-if-kde-used-windows-10-design-components/)
there you also have the menu starter and some additional widgets in
the starter so maybe we can extend the panel to an widget container or
make an widget container, where the user can add and remove stuff.

I'm not a big fan of different desktop shells cause the only
difference is that you have different widgets so the user should say I
want that widget and fine.