Show a different icon for bookmarked stops in the map view.

Show a different icon for bookmarked stops in the map view:
![2014-07-05 13 41 44](https://cloud.githubusercontent.com/assets/536584/3487535/7452f47a-0485-11e4-98c8-635a966444ab.png)

Part of feature request for 2.3:
https://huboard.com/OneBusAway/onebusaway-iphone/#/milestones/issues/6255628

The bookmark color can be tweaked if needed.