Adds contextSelector to attachTo and select

After participate in a discussion at the Flight's Google Group, "[Component granulation](https://groups.google.com/forum/#!msg/twitter-flight/BgAog5RW5us/was8OnMqiz4J)", I have developed a possible improvement to attachTo and the select method. Adding contextSelector as an argument to attachTo and using it as a string to get the closest selector.

The main goal is the posibility of delegate components to a main container. That means, less components to initialize and less events to listen.