Attach subject footer to e-mail (#264)

I added the footer requested in #264, as well as a default subject of "OneBusAway iOS feedback." 

Here's what it looks like when you click the link from the app:
![img_5073](https://f.cloud.github.com/assets/4627278/2177438/0d7892c6-9619-11e3-96ff-94e66f9298e8.PNG)

Note: Getting the exact model (e.g, iPhone 4, iPhone 5) is more of a hassle than it should be, but if we think it's important I can get that in there too. Also, is the ```passive``` and ```5.0w``` label important? I noticed the location data includes some data about if they are currently moving and if so, how quickly, but it didn't seem as important. 

@barbeau Let me know if this looks good!