[SwitchBoard] Find view by react tag fast and guaranteed and on main thread.
[SwitchBoard] Find view by react tag fast and guaranteed and on main thread.

Fixes #88.

artsy/eigen,artsy/eigen,artsy/emission,artsy/emission,artsy/emission,artsy/emission,artsy/eigen,artsy/eigen,artsy/emission,artsy/eigen,artsy/eigen,artsy/eigen,artsy/emission,artsy/emission