Add support for Postgres Transactions

[Fmstrat]

Is your feature request related to a problem? Please describe.
Unless I am missing something, there is no way to use transactions to interface with Postgres: https://www.postgresql.org/docs/8.3/tutorial-transactions.html

Describe the solution you'd like
The ability to use transactions, for instance, highlight and run:

BEGIN;

Then highlight and run:

SAVEPOINT my_savepoint;
UPDATE accounts SET balance = balance - 100.00 WHERE name = 'Alice';

Then highlight and run:

ROLLBACK TO my_savepoint;
COMMIT;

And have the DB be where it was when it started.