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.
Okay, but the relevant credentials are already in memory and will be used
when reopening, right?
On Oct 27, 2014 5:36 PM, "adamrp" <notifications@github.com> wrote:

> In qiita_db/sql_connection.py:
>
> > @@ -57,6 +71,10 @@ def get_postgres_cursor(self):
> >
> >          Raises a QiitaDBConnectionError if the cursor cannot be created
> >          """
> > +        if self._connection.closed:
>
> some things, e.g. the qiita_env CLI commands, use the admin user
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/biocore/qiita/pull/512/files#r19445305>.
>