DataFrame.to_sql generated text field that could not be used by "group by". (MS sql)
In `_sqlalchemy_type` function, pandas import Text type from sqlalchemy as the default type when generating text field in SQL table, which is transformed into "text" type in microsoft sql. This type could not be used by "group by" in SQL query. 
SQL query with a group by clause with the field generate an error msg like:

Msg 306, Level 16, State 2, Line 3
The text, ntext, and image data types cannot be compared or sorted, except when using IS NULL or LIKE operator.

I tried default text field to be the `String`, which works for MS sql.
