List all external dependencies in the ref docs

As discussed in this threads http://lists.springsource.com/archives/springpython-users/2009-October/000102.html,
http://lists.springsource.com/archives/springpython-users/2009-September/000093.html, no external Spring Python's dependencies are currently documented which makes it hard to get started with SP. For instance, after reading the DatabaseTemplate docs, one still doesn't know what needs to be installed to be able to connect to any of the databases mentioned.

The goal of this ticket is to list all the dependencies for each of the core components' docs.