templates: add namespace to differentiate admin and core

As per the django documentation we should create namespacing if templates
with the same file name exists in different dirs. Django picks the first
one by default:

"Django will choose the first template it finds whose name matches, and if
you had a template with the same name in a different application, Django
would be unable to distinguish between them. We need to be able to point
Django at the right one, and the easiest way to ensure this is by
namespacing them. That is, by putting those templates inside another
directory named for the application itself."
Home: home template doesn't use base template anymore
Home: insert nav bar
Home: insert sign up button at the header
Home: add rewards row