Minimal changes to interface/callbacks, all of the changes are
internal and prepare for MSIM.
Separate out AccessPoint and MobileData from the NetworkController
interface to give some space.
A SignalController class has been created as a base for both
WifiSignalController and MobileSignalController, both of which
internally handle the state of their respective connectivity and
only reach up into the NetworkControllerImpl when completely
necessary (such as for combined carrier label).
Bug: 18222975
Change-Id: I75b954bbece187371cdb8571dd8420e7d2cad978
d2263cd9db