Polls

Closes #1 (closed).

Extra additions and clarifications:

• Refactored breadcrumbs with a generic component. This is still not as reusable as I want it to be. I think the breadcrumbs work great for navigation, and I'd like to see them implemented across the website.
• Requires formset_class in create_formset_post_data. No reason not to, and it can be used to get the form prefix
• Uses a database trigger to enforce poll type immutability, since changing a poll's type invalidates votes. Uses django-pgtrigger. This is experimental, but I really like what triggers are able to do. They might also be useful for #15 (closed).
• The poll results page doesn't look very good, though it's easier to see the percentages now than before. I didn't want to spend too much time on this.
• There is no good way to navigate to polls. A link in the navbar can wait for #104 (closed), though we also need to make the latest poll visitable and votable on the front-page.
  • Should the latest poll be on the dashboard, or should we re-implement the sidebar from the old website? This is an open question, though I think something like the old sidebar is the correct answer, since the latest public poll should be viewable by anonymous users. Again, didn't want to spend too much time on this.