Several plugin improvements

I modified the plugin to meet the needs of our javascript application. Perhaps you can use it.

**Features:**

- Loads the Google Maps API asynchronously when it's not already present.
- `$.fn.GMapsLatLonPicker()` has been added to enable external scripts to initialize new maps.
- `location_name_changed` event now has an extra parameter: `result[0]` of the Google Maps address matches.
- Search field now searches when pressing [Enter].

**Bugfixes:**

- `gllp_perform_search` and `gllp_update_fields` events are no longer bound on the `document`. Instead uses the CSS ID of the wrapper div. This prevents maps from updating when they are already removed from the DOM (would result in "too much recursion" errors).
- Global `console.log` call has been removed, for the sake of not cluttering the console.