Make MsSqlDialect compatible with AzureSql and READ COMMITTED SNAPSHOT

[fschmied]

NEventStore's SqlPersistenceEngine relies on database-level locks when reading commits. When one enables SQL Server's READ COMMITTED SNAPSHOT option at the DB level, this stops working and there's a high possibility of skipping commits. On Azure SQL this option is always on, so one will easily experience lost commits on Azure SQL. This was reported previously, e.g., in #14 or #21 (comment).

To cope with that, the MsSqlDialect should use READCOMMITTEDLOCK table hints when reading commits to enforce locking.

[fschmied]

It should suffice to just replace all the FROM Commits strings in the SELECT statements for reading commits with FROM Commits WITH (READCOMMITTEDLOCK).