Allows informing the connection manager of additional information on CQM
events. Allows the connection manager to request the same information
on demand by using the existing "SignalPoll" method.
* Add new property "SignalChange"
* Add storage for wpa_signal_info into wpa_supplicant context
object
* Copy memory from event to context object on CQM Event
* Write a common conversion method to be used by both "SignalPoll" and
this property
Signed-off-by: David Ruth <druth@chromium.org>