Debugger: Switch on "column resize to contents" by default

Since it's easier to shrink columns nowadays (left click
on header section or somewhere in the empty space) this
might "feel" better than last time we tried.

This is an experiment for now, might get reverted before 3.2.

Task-number: QTCREATORBUG-9918
Change-Id: I379d9310e232a16c8b8ee3c6cb0d91746fd7553c
Reviewed-by: Eike Ziller <eike.ziller@digia.com>