Do not show empty collections in container, masthead and sectionZone

@ironsidevsquincy Ping!

This now will not show a section tag in each template (`masthead`, `sectionZone` and `container`) if the `Collection` coming in has got no items in it.

The diff is a bit crazy, all it is really doing is wrapping each `section` with an `@if(collections.items.nonEmpty)` and indenting all the code.