Install imagemagick in vagrant vm.
Add refinery-banners engine.
Fix styling for banners

- Put banners in center of container
- Set minimum size of page and elements to make room for banners
Render banners from layout instead of modifying all views.
Display published ads instead of active.

This means that ads will only be shown between their start-publishin
date, and their end-publishing date. They will also only be shown on
the pages where they are enabled. This allows different ads on different
pages, or ads only on some pages, while others completely without ads.
Merge branch 'banner-ads'