Analytics: Create a generic API in AppDelegate class

And move all Google Analytics code to AppDelegate.m

Riot/ViewController/RoomSettingsViewController.m

@@ -264,14 +264,9 @@ NSString *const kRoomSettingsAdvancedE2eEnabledCellViewIdentifier = @"kRoomSetti
 - (void)viewWillAppear:(BOOL)animated
 {
     [super viewWillAppear:animated];
-    
-    // Screen tracking (via Google Analytics)
-    id<GAITracker> tracker = [[GAI sharedInstance] defaultTracker];
-    if (tracker)
-    {
-        [tracker set:kGAIScreenName value:@"RoomSettings"];
-        [tracker send:[[GAIDictionaryBuilder createScreenView] build]];
-    }
+
+    // Screen tracking
+    [[AppDelegate theDelegate] trackScreen:@"RoomSettings"];
     
     [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didUpdateRules:) name:kMXNotificationCenterDidUpdateRules object:nil];