Draft: Save and restore sessions

Retrieve MR !11 made by @mschiller, rebase on master, fix compiling error and coding style.

In draft because:

• I investigate on comment !11 (comment 324964)
• sometime when Yakuake is closed with Exit menu the configuration is wrongly saved: CurrentWorkDir is empty and Title value is - : (except for the last tab)
• I'm adding option to choose the default working dir when a new session is created

I also want to restore the history if possible. But for now I don't know how to do that... I will probably dissociate that from this MR.