Shuttle card breakout

[srkirkland]

@a6wu Pretty big refactor of Shuttle Card out of Home.js. Could still use some work to update the logic to allow a different number of shuttles than just two and other features, but I think it works as well or better than the old one. It is a bit different because of a few reasons:

• doesn't load until an actual location is found. Maybe we'll want to change it to use a default location but I do not think that should be the card's concern, and also I don't think it should be hardcoded anyway.
• card now updates when the this.state.currentPosition changes lat/lng. Depending on how agressively you are tracking the user's location in the future we might want to meter/debounce this but for now it's pretty cool.
• uses setInterval() for a timer which seems to work very well, instead of the old mixin.

pretty much closes #30

[i8wu]

Since the card now refreshes on location change and on an interval we may want to change logic so Home.js refreshAllCards() isn't also refreshing it. Will take a look when I've got a bit more time. @c3bryant thoughts?

[c3bryant]

@i8wu after v2.3 it might be a good time to revisit building a Feed Manager of sorts that all views use, leveraging AsyncStorage to keep track of feeds/timestamps so we can use caching and have an overall better handle on what/when which feeds are being refreshed

[jpknoll]

@c3bryant Disagree re: global feed manager. Cards can/should manage their own data access via a thin service layer. If you want caching, it should be implemented there.