custom loader for mssql

[timandrews335]

Hi,
I was looking to contribute a custom loader for mssql, similar to the existing mysql custom loader. It would address two issues:

1.) suppressing the nonsense built-in schemas like "db_owner," "db_datawriter," etc (9 total) from the list of schemas returned that just clutters up the UI.

2.) adding support for tables to be returned in the UI, which are currently missing from pymssql / base sqlalchemy loader.