Add OS X target

Rearranged the project a little bit and added an OS X target so that
this can be used for mac apps.
Run Liftoff on project

This updates the project settings with our recommended defaults.

Notable exception is that we're setting the indentation to 2 spaces
instead of 4.
Add tests to scheme test actions

This allows us to run the tests under the scheme with the `command + U`
keyboard shortcut.