Creators can set project "shorturl" codes

[bhaibel]

As a creator
I want to be able to set a shorturl/slug for my projects
So that I can direct folks to https://nourish.party/contribute_to/space_unicorns instead of scaring them off with a UUID-containing URL.

[zspencer]

Any feels re: how the following scenarios should play out?

Scenario: Visiting a project which has a slug via the UUID
Scenario: Visiting a project without a slug
Scenario: Changing a projects slug
Scenario: Visiting a project which has a slug with an old slug

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