Debugger: Force reset of "Load system GDB pretty printer" option

Using them still bites often. Since we can't distinguish between
setups run first with Creator 3.1 (where the option was 'on'
by default) and people who actively selected that at another
time, reset for all. People _needing_ them can opt in again.
There won't be many, if at all.

Change-Id: I68c64d71f0c8ab4a3e6c73cc91481a7d3f9ef6b9
Reviewed-by: Eike Ziller <eike.ziller@digia.com>
TextEditor: static-ify plugin class

Change-Id: Id795b711f08c89b6066c5269c482fea5e99dd52f
Reviewed-by: David Schulz <david.schulz@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>