Add removeObjectForKey method to IASKSettingsStore protocol.
Also implement this method in File and UserDefaults Settings store.
Improved subclassing of IASKAppSettingsViewController

by not removing all notification observers but just the ones we added
Merge pull request #225 from olicarbo/upstream

Add removeObjectForKey method to IASKSettingsStore protocol.
Ignore .xcuserdata
silence compiler warnings when implementing custom settings store (by @mman)
Fixed removal of NSUserDefaultsDidChangeNotification

close #234
Sample App: iOS 7 modifications

close #224
Support ShortTitles for Multi Value Elements (introduced in IOS 5.0)

thx @meizy
Fixed warnings and modernized build settings