#306 Regions plugin is required by core classes

[Olly Burren]

GDxBase::Persistable::Region requires a join across the region database and curate database. This routine is called by GDxBase::Persistable::Study::get_gwas_data (part of core). This is inturn called by GDxBase::Section::Study::get_html. At the moment this is OK as region is always installed however when working out dependencies between databases it can be a little confusing. There are a few options to consider.

1. Test to see that region plugin is installed if not ignore - however this still means that core and plugin are intertwined
2. Write a script (preferably part of setup.pl) that moves the correct tables from curate to regions database. Rewrite the query so that SQL uses local copy of these tables. We would also need to implent 1 as core and plugin code are still mixed.