Use DEVELOPER_DIR instead of SYSTEM_APPS_DIR

This fixes compilation if Xcode was renamed.
quick fix for issue #14, this prevents just the crash and does not solve the origin of the bug
Remove < Xcode 5.1 compatibility. Closes #13.
Create the themes directory before installing them

[Fixes] https://github.com/kolinkrewinkel/Polychromatic/issues/19
Code style fix for theme directory stuff.
Merge 0xced branch. Not sure what just happened with git.
Merge pull request #22 from kolinkrewinkel/polychromatic-v1.0.1

Polychromatic v1.0.1.
Git-ignore Xcode litter