WIP - DO NOT MERGE: Experimental, Multiple Splits per Tab

Summary:
This is what I envision for the Konsole Tab / Splits
management. One tab contain a QSPlitter that can contain
multiple TerminalDisplays / Splits.

You can test this behavior by hitting ctrl + shift + 9
and ctrl + shift + 0 to activate the splits, and ctrl +
shift + t to activate a new tab.

What works:

• Tab Creation
• Split Creation (Even Recursive splitting)
• Terminal Close will close the Split on last split
• Last last split to close will close the tab
• Last tab to close will close konsole

This is *highly broken* as too many things don't work yet:

• Detaching will not work
• Reataching will not work
• Tab Naming will not work

Probably a few other things too.

I plan to update this as soon as I remove some of the known bugs

Subscribers: konsole-devel

Tags: Konsole

Differential Revision: https://phabricator.kde.org/D17643