[AI-409] Extend customization to all freemarker-rendered pages

Refactored CSS:
- Reverse engineered Naina's theme back into less files, see
  /style/less
- Changed all container-fluid and row-fluid to container and row styles
  (we didn't need them- container and row are responsive as well)

Replaced DomainProvider with Provider<Domain>
- Easier to bind in tests with Providers.of(Domain.DEFAULT) for example

Pushed domain logic to presentation layer
- Domain is shared variable across all templates, page and mail, so it
  doesn't have to be added to all page/mail models
- Introduced ScaffoldingDirective, which allows us to skin all pages with
  a custom scaffolding pulled from the database

Added sign up permissions to domain table

Added simple form for updating scaffolding / front matter:
  http://www.activityinfo.org/admin/branding/{domain}