Revert "ENYO-2899: take into account comments by @graynorton & @unwiredben"

This reverts commit 3185d061fb2a5fc1fa130f419a48b676965ef5db.
ENYO-2899: take into account comments by @graynorton & @unwiredben (2)

- Create `Ares.Model` as a singleton, so that it can be freely
  manipulated to host more `Backbone.Model` templates.