Build phase scripts to manage bundle build version and bundle identifier

This includes three build phase scripts described in #16: 

* Set the bundle version number to the [current git commit short SHA](http://stackoverflow.com/a/949391/2120699) using the command `git rev-parse --short HEAD`. If the git working copy has [dirty changes](http://stackoverflow.com/a/2659808/2120699) then a plus is appended to the build number to indicate dirty changes in the build.
* Set the bundle identifier to `org.onebusaway.iphone` if the current build configuration is `AppStoreDistribution`
* Delete the bundle version and reset the bundle identifier to `org.onebusaway.iphone.dev` for clean git commits.

I also modified the Settings view to include the build number. Here is a screenshot of the Settings view with dirty changes:
![img_0018](https://f.cloud.github.com/assets/498432/1160603/8b6b8328-1fdb-11e3-873b-3b7ec5352990.PNG)

... and without dirty changes:

![img_0019](https://f.cloud.github.com/assets/498432/1160620/d2a5b3c6-1fdb-11e3-8baf-17037e05160a.PNG)