Add a new category collection for MapKit-related work. This commit adds a pair of functions which take an NSSet of NSValue objects containing CLLocationCoordinate2D structs and outputs a MKCoordinateRegion (with the specified percentage padding).
Set the region to make sure it only encompasses the two annotations we care about.
Strip out a large amount of duplicated code for calculating map regions. Just create a list of  NSValues containing the CLLocation coordinates and pass it off to the new MapKit helper function.
Tweak the view rendering code a bit more. This is mostly to prevent the app's death if it's handed an invalid frame rect
Rename the NSValue category methods so they don't conflict with iOS6's built-in methods. This will save us quite a few headaches later
Switch to using the MK* based methods for calculating instead of the ArcGIS classes.

ToDo: make a note to ArcGIS regarding convertValue:fromUnit: as it crashes the app without any sort of helpful messages