* Added basic infrastructure to layout user preferences. The
intention is that you open a user preferences space in place
of the buttons space, and have panels there.
* The existing sections don't have to be followed, it's easy
to create different ones, just change the user_pref_sections
enum in RNA.
* This will get separated from the info header later.
Image Window
* Unpack operator now works.
* Some small layout code tweaks.
Info Window Header
* Moved to python UI code.
* template_running_jobs, template_operator_search added.
* Ported external data operators: pack/unpack all, make
paths relative/absolute, find/report missing files.
Also
* Report RPT_INFO too, not only warnings and errors.
* Run UI handle functions after RNA and Operators.
* Rename particle system add/remove operators, to not
include "slot", that's only there for materials because
that's what they are called now in RNA.
