All python render controllers now inherit the functionality of DefaultRenderController
use appleseed.python gil lock class, don't copy the locking code.
reverted unjustified changes to test scene.

changes introduced in 1e927e10abe67801de53e2c929c5ef49845d9ab7 ("Improving searchpaths support").
fixed a number of issues found in recent search paths commits.

- during file lookup, search in the root path only after searching in the other paths failed.
- fixed writing of search paths in project files.
- renamed iterators to conform to std:: standards.
- don't expose std:: types in foundation::SearchPaths methods.
- fixed cosmetic issues.
fixed styling issues.
cleaned up the API and simplified the implementation of foundation::SearchPaths.
Merge pull request #284 from est77/more_py_fixes

More appleseed.python fixes
updated URL  in documentation.
fixed formatting.
made renderer::InputBinder::find_entity() static.
fixed coding style.