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.
Can't tolerate db config reloads then, I thought qiita only had a user
level db connection too?
On Oct 27, 2014 5:11 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:
>
> If the connection is closed, i think this should just raise an exception
> rather than create a new connection, since it cannot tell whether it should
> be an admin connection or not
>
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> <https://github.com/biocore/qiita/pull/512/files#r19444270>.
>