issue 879 source maps

issue #879
@gitnik
@aesnyder
@cthrax 

In process in working on issue 904 I decided I had enough with the large file. So now we have sourcemapping at all kinds of levels.

I do not plan on commiting the tmp/ directory (where the maps point to) as this will cause more merge problems. However if someone can
convice me otherwise then we can add tmp/. 

Please review.

With this change `grunt mappAll` will yield:
- dist/angular-google-maps.js
- dist/angular-google-maps_dev_mapped.js
- dist/angular-google-maps_dev_mapped.js.map
- dist/angular-google-maps_dev_mapped.min.js
- dist/angular-google-maps_dev_mapped.min.js.map
@aesnyder having a clone fn locally is still less terse but it uses _.extend :)