Refactors google maps loading + jshint offenses

- Loads google maps asynchronously using the example code from the
Google Docs at
https://developers.google.com/maps/documentation/javascript/examples/map
-simple-async
- Moves map plugins to the /vendor/ directory instead of having them
inline. Yes!!
- Removes async plugin as it is no longer needed.
- Fixes JSHint offenses.
- Fixes some Haml style guide offenses.
Merge pull request #576 from codeforamerica/map-loading-updates

Refactors google maps loading + jshint offenses