Query cancellation support is added via CancellationToken mechanisms that
were implemented previously. This change adds a new request type
"query/cancel" that will issue the cancellation token. Unit tests were
also added.
* Adding error flag for Query class
* Adding message capture for messages from server (using SqlConnection
cast)
* Adding better handling of SELECT queries with 0 results
* Adding affected row count message
* Adding SqlError unwrapping (using SqlException cast)
* Removing DbException handling from QueryExecutionService and into Query
class
