Parameterise base configs so they can be overridden.

The standard deployment behaviour doesn't change with this commit, however
it's now possible to override the default config values.  The main motivation for
this is to be able to recurse rDNS lookups, which requires removing the
'bogus-priv' config parameter.

- Introduce a new params class and migrate the defaults that existed in
  the static config files.
- Update the init, client and server classes to deploy their relevant
  config files from templates, taking their values from the new params
  class.
- Remove the old static config files.
- Update documentation to reflect the changes.
"Options managed by Puppet" might be clearer.