CSHARP-1071: Add ListIndexesOperation.
Deleted IndexExistsOperation (use ListIndexesOperation instead and examine the result to see if the index exists).
CSHARP-1079: added support to core for authMechanismPropertis
added authMechanismProperties to high level API and corrected issue with SCRAM not being used from high level api.
all connection string parsing is now handled by the core ConnectionString class. MongoUrlBuilder does not do any parsing.