Stub file imports

- create import statements for frameworks defined in the Rakefile
- if no frameworks are defined default to the original headers

Note that the spec still passes because there is no Rakefile config set in the specs.  I did not add that to the specs, but can confirm that this works in the iOS RubyMotion app that I wrote this patch for.  I'm running the code locally.  Now I can define outlets that use MapKit where before those headers were not available unless I manually edited the stub header file.