ensures that escaping in the sql expression classes is done correctly without any double escaping. Also ensures that escaping is happening using the equals operator, not just the Equals() method and adds unit tests for them.
Fixes: U4-4232 Umbraco.Core.Persistence.Querying issue with backslashes
Adding a MediaTypeMapper similar to the ContentTypeMapper, but type specific.
The PetaPoco IMapper implementation is removed as its no longer needed.
Updating a few unit tests, as the Where clause is now correctly formatted.
Adding unit tests for the new ExpressionHelper and MappingResolver classes.