Fix issue #1011 - adds touchable event handlers to text

[DaKaZ]

This is my second attempt to close issue #1011. This borrows much from the react-native Text component (https://github.com/facebook/react-native/blob/master/Libraries/Text/Text.js) but modifies the approach to handle web specific events like mousedown and mouseup and mouseout.

[DaKaZ]

@necolas did you want me to update this PR... just let me know

[necolas]

Thanks for this PR, it looks good. However, I've been thinking about this feature for a while, and I think I'm going to keep it excluded from web by design. Apps like Twitter are using Text everywhere and adding the build and runtime overhead of Touchable to Text is (on balance) going to make the most common use of Text become more expensive. I think RN is doing too much in Text (it didn't use to overload it with press functionality either) vs View, and RN should probably redesign its exports to include something like TouchableText.