Easier changing of settings for local development.

Create a local.py in settings/ - it has access to the current settings.
Update Section title to heading.

Follow on from changes in the SayIt app to have num/heading/subheading.
Fix traceback on instance homepage.
remove old homepage content and styles
new homepage copy and basic layout
add images to marketing homepage
remove unused images from old homepage
add helpful links to nav bar
Use staticfiles and translate alt texts.
Shift comma to outside the Poplus component link
Better text for create instance link.

Also keep this text consistent for logged in and not.
Change a few links to go to the base host.

The /about and instances/add links need to be to the base
vhost rather than to the current instance.