Add sponsors to front page and add sponsors profiles.

calpoly/frontend/frontend_misc.py: Get 3 random sponsors.
calpoly/frontend/sponsors.py: Add sponsors profiles.
calpoly/frontend/templates/index.html: Get 3 random sponsors in sponsors section.
calpoly/frontend/templates/sponsors/sponsor.html:
Create template for a single sponsor.
calpoly/frontend/templates/sponsors/sponsors_index.html:
Fill in sections regarding the branch itself.
calpoly/sponsors/models.py: Remove unneeded
fields.