redo BITAuthenticator interface

given the good feedback we got, this is take 2
of the BITAuthenticator interface.
It's simplified, cleaned up and now allows full
control over the authentication process.
Major changes:
* manual mode
  Authenticator provides the bits to show the
  viewController to identify the user as well as to
  trigger validation on behalf of the developer.
* process separation
  identification and app-usage-restriction are now
  2 completely separated things.
* public identifier
  Authenticator now allows the developer to query
  parts of the information, e.g. the UDID or the user's
  emailaddy once identified

Classes/BITAuthenticationViewController.h

@@ -54,14 +54,12 @@
  */
 @property (nonatomic, assign) BOOL requirePassword;
 
-/** configure if user can skip authentication or not
- *
- *  defaults to YES
- */
-@property (nonatomic, assign) BOOL showsSkipButton;
-
 @property (nonatomic, weak) id<BITAuthenticationViewControllerDelegate> delegate;
 
+/**
+ *  allows to pre-fill the email-addy
+ */
+@property (nonatomic, copy) NSString* email;
 @end
 
 /**
@@ -69,13 +67,6 @@
  */
 @protocol BITAuthenticationViewControllerDelegate<NSObject>
 
-/**
- *	called then the user skipped the auth-dialgo
- *
- *	@param	viewController the delegating viewcontroller
- */
-- (void) authenticationViewControllerDidSkip:(UIViewController*) viewController;
-
 - (void) authenticationViewControllerDidTapWebButton:(UIViewController*) viewController;
 
 /**