Adding several stubs for upcoming features

  * Adding a place to handling theming (WIP)
  * Adding basic engine setup via host app inititializers
  * Making root path in coffeescript dynamic
  * Separating engine into front and back end engines (WIP)
  * Setting up infrastructure for authentication solutions from host app (WIP)
  * Spacepub::Admin Engine to replace Spacepub::Engine for admin interactions (WIP)
  * Spacepub::Front Engine for future front end interactions (WIP)