Since we're using jinja, I figured we ought to use jinja... …

- jinja environment has been set up for template loading
- since the two templates we made were both using bootstrap 3,
  I merged them into a base template so future htmlers can benefit
- areas that use jinja templates use the new `utils.datafile.template_env`

Depends on #332, which should (maybe? hopefully?) drop the related commit from this pr.