add testing for ConsensusConflict type
add testing for ConsensusConflict type

The consensus conflict type has been in use for a little while, but
without unit tests. There are now unit tests to confirm the correctness
of the ConsensusConflict helper functions and general usage.

ericflo/Sia,NebulousLabs/Sia,mtlynch/Sia,mtlynch/Sia,rivine/rivine,mharkus/Sia,ChrisSchinnerl/Sia,ericflo/Sia,rivine/rivine,johnathanhowell/Sia,NebulousLabs/Sia,mharkus/Sia,MrStrong/Sia,ChrisSchinnerl/Sia,mnsl/Sia,mnsl/Sia,MrStrong/Sia