iOS 7 support

This is the nearly-complete iOS 7 support for the SDK. There are some smaller remaining items, deleted below. 

### Changes

 * iOS 7-style user location dot, `RMUserTrackingBarButtonItem`, and callouts. 
 * Global `tintColor` support, including dimming. 
 * `RMPointAnnotation` markers now also follow the `mapView.tintColor`. 
 * Moves from a page curl transition to either a translucent, slide-up modal (iPhone) or a popover (iPad) for attribution info. 
 * Added an activity indicator when loading the attribution content `UIWebView`. 
 * Updated background grid view behind loading tiles to look better. 
 * Support for top and bottom `UIViewController` layout guides. 
 * Added tappable compass image during map rotation. 
 * Fixed a bug with requesting MapBox `RMMarker` objects tinted with colors in non-RGB color spaces. 
 * Now requires Xcode 5.0+ for access to iOS 7 SDK. 

### Remaining

 * [ ] Animation of `RMUserTrackingBarButtonItem` background color shouldn't happen. 
 * [ ] User location dot doesn't pulse. 
 * [ ] User heading accuracy wedge still showing iOS 6 style; needs to be a tinted gradient. 
 * [ ] Need to build out a distance scale view for when the user is zooming. 
 * [ ] Slight bug in attribution modal on iPhone during device rotation (https://devforums.apple.com/message/873505). 
 * [ ] Callouts can occasionally appear under the navigation bar. (https://github.com/nfarina/calloutview/pull/52)
 * [ ] Callout appearance animation needs tweaks. (https://github.com/nfarina/calloutview/pull/52)
 * [ ] User location dot shadow could use some very minor tweaks.