SP-1174 - Regression of BISERVER-11142 - Staging table not getting deleted when a datasource created using CSV File of Data Source Wizard is deleted (5.0)

What was done:
1) fixed issue with deserializing model
2) added check for CSV model
3) added call to remove CSV model
Merge pull request #412 from kolinus/SP-1174-2

SP-1174 - Regression of BISERVER-11142 - Staging table not getting delet...