Fix broken behavior in case of texcoords mapping (we do need texcoords
node in all cases, then, even for UV coords...).
Use nodes by default when generating new write-allowed wrapper around a
material.
Do not try to find nodes in existing tree all the time, do it only once,
even for lazy-initialized nodes (through accessors).
Fix ugly spacing in property accessors (since it looks like some people
do not like a single 'block' with both getters, setters and prop
definition, at least use one sep line everywhere (and two sep lines to
separate properties)...