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.
You can actually support `executemany` here: you add an extra parameter: `many=false`. If it is true, you replicate the sql statement as many times as needed in the queue, it will simplify a lot the code in other sections :smiley: 

Also, it will support executemany with returning values, something that is not supported on the default postgres.