Add ReactiveCocoa as a submodule and dependency for the iOS app.

Also add an iOS-specific README.md with some necessary
steps for compilation.
Simplify MasterViewController logic with RAC.

Note that there is no longer any throttling.
Update copyright header.
Improve RAC-based network requests searching for people.
Show the network status indicator while searching.

Also, do not change the search results when the text field is cleared.