Profile support for LXQt

[agaida]

implemented like the former LXDE session profile switch. Missed it only sometimes right now - but it would really nice to have.

Refs: https://forum.lxqt.org/t/lxqt-session/266/8

[tsimonq2]

To extend this, it would be nice to have a full UI which would function similar to:

1. Have a "default" profile which is the distributed profile. If the distributor changes a setting, the change should also be made to the profile on the next login after the update.
2. Allow users to customize, create, and duplicate profiles through the GUI, having the ability to give it a name, icon, and description.

Maybe a better word is "layout" but hmm, do we want to go as far as to give it control to all settings?

Just my two cents, feel free to give your thoughts.

[tsimonq2]

I'd like to get this tackled in time for Lubuntu 19.04, so assigning to myself.

Would be good to get some extra thoughts on it, so we can discuss these things before I take a jab at implementing it. 😝