Allow loggers and default factories to be set on connection pools

[kgaughan]

This is a silly omission.

Right now, pools don't have a way to assign either of these to their contexts. This makes dealing with the likes of Jinja a touch awkward if you're using a connection pool.

What's needed is something akin to the default_factory and logger attributes on Context to be added to PoolBase. These would be assigned to any newly created contexts within the pool.