fix service handling

[kived]

1. Private service does not work. Public service also does not work when specifying a private folder. PythonService seems to always look in the public folder, and the handling in build.py was poor anyway (e.g. always using private dir, without even checking for a private/service dir). I suppose it could check both directories, but until build.py passes that information to the PythonService class or PythonService itself checks both locations it wouldn't really matter.
2. Service flag does not get set if there is no main.py, however, main.pyo should be valid as well.

[tito]

Looks great, thanks