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.