chore (test fixtures):

Renames assets fixtures.
chore (test fixtures):

Removes unused `layout-includes.hbs`
chore (tests):

Adds `pages.js` and `rel.js` helpers for tests.
chore (tests):

Reorganizes, adds, and updates test fixtures to be much more informative.
feature (originalLayout):

Exposes `originalLayout` variable so that the name of the layout being used for each page is accessible to templates
refactor (assets):

Externalizes logic for calculating `assets` path. Also removes code for `removeHbsWhitespace`, since this belongs in a plugin, helper or something else.
chore (tests):

Rebuild with new fixtures and Gruntfile targets