Ensure map options are respected after free-drawing polygons

Resolves #952.

It's a bug fix, because there was already code in there to revert the map options after drawing, but it wasn't quite working the right way.

Changes:

* Use `@oldOptions = map.getOptions().options` instead of `@oldOptions = map.getOptions()`.
* Use `@map.setOptions _.defaults @oldOptions, enabledMapOptions` instead of `@map.setOptions _.extend @oldOptions, defaultOptions`.
https://github.com/angular-ui/angular-google-maps/blob/master/src/coffee/directives/api/map.coffee#L221-L223