main.py some cleaning in init()

units.py

more info in call UnitSystem

add phot module

routines to convert Magnitues in luminosities

more examples for units module

examples/units/setunits_5.py
examples/units/setunits_6.py

git-svn-id: https://svn.epfl.ch/svn/pnbody@69 f1771ac9-52fb-4361-9f77-cbfb7563c7d4