Use Amazon CloudFront for static hosting

[taylortrimble]

• Adds a function for generating a CDN URL from a "relative" app URL
• CDN URL uses versioning, which lets us set absolutely massive max-age
• URL util is made available to Jinja

Current testing shows that Amazon CloudFront takes much longer than our own static hosting.

Our Typical	CF Typical
500ms	850ms

The catch is, I don't think this is actually typical, only typical right now. I think that usually our server gets slammed at certain times of the day and static hosting slows to a crawl. AWS gives us more consistency, at the cost of best-case.

Also snuck in a util function location refactor.

:warning: Necessary Update Path

Before deploying this, we must:

• Automate or document the process that modified static resources are given a versioned URL prefix and uploaded to S3
• Remove the /static/ prefixes from our URLs in the database:
  • photo_url in projects, leaders, and project_photos
• We should come up with a system for deleting old static data to avoid (admittedly tiny) excess storage costs

[taylortrimble]

Oh yeah, and more load time testing to come.

[taylortrimble]

This was informative, but not a success. I'm leaving this open so we can improve off of it, but this shouldn't be pulled as-is, and until we have a good static solution spun up.

[taylortrimble]

Nah.