Add transaction blocks

This adds transaction queue functionality to the SQLConnectionHandler. There is the ability to have multiple queues per connection handler, as well as the ability to use returned values from a previous sql query in subsequent queries in the queue.
Queues are created using the `create_queue` method and then added to using the `add_to_queue` method. Calling `execute_queue` executes the queue, as expected.
To use previous result values, you need to know the order a previous query returns in. Then, you can use a similar format to the string format function to insert these values. The tests added give a good example of this functionality.
The inner one is needed because if we execute a command that doesn't return anything, then go to fetchall, psycopg2 raises an error. Unfortunately this is a generic `Error`, so I can't catch anything specific. The inner try-except basically makes the function ignore failures if there is nothing to fetch.