Change LogContext.PushProperties to accept ILogEventEnrichers rather than just PropertyEnrichers

(cherry picked from commit 1c41ab8fc8dcf0e4526365550ae9d8b0a33890a3)
Merge pull request #342 from richiej84/Custom_PropoertyEnricher_Support

Change LogContext.PushProperties to accept ILogEventEnrichers rather tha...