Early handshake fail #121
Description
Context
It happens often that first side that knows about failed connection is actually the Callee (RTC Connection state changes to failed). It takes some significant time before the other side's (Caller) RTC Connection does the same.
What
Callee to send via Signaling server info to Caller that connection failed; so he can try retry faster.
Risk
It may cause some conflicts with #120 ; e.g. connection can fail, but if the process of gathering ice candidates haven't finished, we should keep trying