Generate and send time request CoAP message
Call set time callback on server time response
Merge branch 'master' into feature/set-time-from-cloud

Conflicts:
	src/spark_protocol.h
	tests/ConstructorFixture.cpp
	tests/ConstructorFixture.h
Merge pull request #16 from spark/feature/set-time-from-cloud

Set device time from Spark Cloud