AppRTCDemo(iOS): remote-video reliability fixes

Previously GAE Channel callbacks would be handled by JS string-encoding the
payload into a URL.  Unfortunately this is limited to the (undocumented,
silently problematic) maximum URL length UIWebView supports.  Replaced this
scheme by a notification from JS to ObjC and a getter from ObjC to JS (which
happens out-of-line to avoid worrying about UIWebView's re-entrancy, or lack
thereof).  Part of this change also moved from a combination of: JSON,
URL-escaping, and ad-hoc :-separated values to simply JSON.

Also incidentally:
- Removed outdated TODO about onRenegotiationNeeded, which is unneeded
- Move handling of PeerConnection callbacks to the main queue to avoid having
  to think about concurrency too hard.
- Replaced a bunch of NSOrderedSame with isEqualToString for clearer code and
  not having to worry about the fact that [nil compare:@"foo"]==NSOrderedSame
  is always true (yay ObjC!).
- Auto-scroll messages view.

BUG=3117
R=noahric@google.com

Review URL: https://webrtc-codereview.appspot.com/10899006

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5814 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/examples/ios/AppRTCDemo/APPRTCViewController.h

@@ -32,9 +32,9 @@
 // The view controller that is displayed when AppRTCDemo is loaded.
 @interface APPRTCViewController : UIViewController<UITextFieldDelegate>
 
-@property(weak, nonatomic) IBOutlet UITextField* textField;
-@property(weak, nonatomic) IBOutlet UITextView* textInstructions;
-@property(weak, nonatomic) IBOutlet UITextView* textOutput;
+@property(weak, nonatomic) IBOutlet UITextField* roomInput;
+@property(weak, nonatomic) IBOutlet UITextView* instructionsView;
+@property(weak, nonatomic) IBOutlet UITextView* logView;
 @property(weak, nonatomic) IBOutlet UIView* blackView;
 
 @property(nonatomic, strong) APPRTCVideoView* remoteVideoView;