Markers with arrows

This is an experiment by @boonrs and I that uses the marker icon as a way of showing the line direction. The current marker icons are terrible but you should get the idea.

![screen shot 2014-05-06 at 10 25 08 am](https://cloud.githubusercontent.com/assets/51882/2892368/272de38a-d53c-11e3-9e76-0be3fc6e44e5.png)

Remaining Tasks
- [ ] Cleanup the WIP commits.
- [ ] Figure out why [this hack] (https://github.com/boonrs/transitmix/blob/markers/app/js/views/markerview.js#L33-L38) is necessary.
- [ ] Redesign the look of the icons.