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
Home: add carousel and finish first version of home page

Download the external resources and add to static folder.
Remove the drawing text animation due to improve performance.
Finish CSS customization.
Course: change Carga horária -> Carga horária e requisitos close #28
Home: add Paula's description
Lesson: change activity column with note column position
Admin message template: fix url bug
Home: remove sign up link
Course: fix 'My notes' url
Header: add light color header and insert mupi logo