Add images & image repositories

Add initial support for images & image repositories.

Add registry webhook to support adding images and tags
to image repositories when a registry's image repository
is updated.
Merge pull request #45 from ncdc/images

Merged by openshift-bot
Implement TemplateConfig endpoint

Adds TemplateProcessor implementation using the default
ExpressionValueGenerator, which is capable of transforming
Template api objects into Config api objects.

Authors:
  Michal Fojtik <mfojtik@redhat.com>
  Vojtech Vitek <vvitek@redhat.com>