Changed inserting into table with trigger to work by default

[jmah8]

• Changes PR Add workaround for insert into table with trigger error #158 so that by default the behaviour of inserting into a table with triggers is the same as in v1.1.2 of mssql-django without changing any settings.
• Introduces return_rows_bulk_insert into the OPTIONS dictionary and removes the has_trigger key, value pair.
• When return_rows_bulk_insert = True returning rows from bulk insert is available
• When return_rows_bulk_insert = False returning rows from bulk insert is not available
• By default return_rows_bulk_insert is set to False
• return_rows_bulk_insert must be set to False to be able to insert into tables with triggers without an error being thrown