Added blurOnSubmit support to multine TextInput (aka RCTTextView)

Summary:
public

Setting `blurOnSubmit=true` on a multiline `<TextInput>` now causes it to behave like a single-line input with respect to the return key:

With the default value of `false`, pressing return will enter a newline character into the field. If you set the value to `true`, pressing return will now blur the field and trigger the onSubmitEditing event. The newline character will *not* be added to the text.

(See associated github task for dicussion: https://github.com/facebook/react-native/pull/2149)

Reviewed By: javache

Differential Revision: D2710448

fb-gh-sync-id: c9706ae11f8b399932d3400ceb4c7558e455570d

Libraries/Text/RCTTextField.m

@@ -36,6 +36,7 @@
     [self addTarget:self action:@selector(textFieldSubmitEditing) forControlEvents:UIControlEventEditingDidEndOnExit];
     [self addObserver:self forKeyPath:@"selectedTextRange" options:0 context:nil];
     _reactSubviews = [NSMutableArray new];
+    _blurOnSubmit = YES;
   }
   return self;
 }