Change url routes to remove pk

[itsthejoker]

Relevant issue: N/A

Description:

When I set up the routes for the posts on the website, I used pk+slug (1-our-story) so that we could have multiple posts with the same name and still tell them apart. That's a great idea as long as the primary key doesn't change, and for some reason it is and the PK of our donations page keeps changing and invalidating its own URL. This PR:

• swaps over to slug only routes
• provides a compatibility redirect layer for the routes we've already publicized -- can be removed after we forget why we added it

Checklist:

• Code Quality
• Pep-8
• Tests (if applicable)
• Success Criteria Met
• Inline Documentation
• Wiki Documentation (if applicable)

[MaxVanDeursen]

We have to make sure that we find out why these PKs are changing though; that does not sound like a feature we want.