Make EasyNetQ.Scheduler work with Devart dotConnect Postgres provider

Just a couple of small tweaks to make the scheduler work with the Devart dotConnect provider.

- Change the SqlDialect class to recognise the dotConnect provider.
- Change the data types for 'work item status' and 'purge batch size' to smallint (to match the postgres data type), since dotConnect doesn't like DbType.Byte.