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.

Old:
{F6484123}

New:
{F6484124}

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
- Detaching
- Tab Renaming
- Closing splits after detach
- Closing windows after detach
- Detach / Reattach works!

This patch series has the commits of Thomas Surrel, Maciej Niedbdalski and Myself.

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: luc4, hallas, anthonyfieroni, gennad, ngraham, thsurrel, maciejn, mglb, hindenburg, konsole-devel

Tags: #konsole

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