Larger numbers of datasets associated with showcase increase load time dramatically

[mattfullerton]

We experience ca. 1 extra second per dataset on uncached showcase pages. The "problem" lies here:
https://github.com/ckan/ckanext-showcase/blob/master/ckanext/showcase/logic/action/get.py#L81

I've spent a while playing with the table modelling around here:
https://github.com/ckan/ckanext-showcase/blob/master/ckanext/showcase/model/__init__.py#L96

to try and make use of the foreign key to the package table so that we can grab the package details (we need name and title for the showcase read template) and not just the IDs so that the for loop of calls to package_show can be removed, but my sqlalchemy skills aren't up to it. Would this be an easy change for someone more experienced?