The node wrangler source code wasn't consistently formatted before,
which made it quite annoying to make changes. This formats it with the
same formatter used for other python files in blender's source code, so
that, in principle, the IDE would already be configured correctly for
anyone working on blender.
After discussion in !104444 and !104457 it became apparent that Node
Wrangler needs a bit of work to make its maintenance more comfortable.
So, split the code into interface, operators and preferences, and a
few specific utility files.
The bulk of the add-on now resides in operators.py.
