Added CatalogueFactory

PLEASE NOTE:

The XROOT plugin (CTA front end) now reads the connect details of
the catalogue database from the following configuration file:

    /etc/cta/cta_catalogue_db.conf

Installing the CTA rpms will install the following example file:

    /etc/cta/cta_catalogue_db.conf.example

This example file document the syntax of the database connect
details.

For the time being the contents of cta_catalogue_db.conf should
simple be:

    in_memory

This means the CTA front end will use an in-memory catalogue
database.