R1:5704b2bc7074

Basic edit/create workflow for Phriction

Summary:
This is another chunk of D636, I just simplified it a bit and added slugs.

When you go to a page like /w/pokemon/, it allows you to create or edit the
page.

Title vs slug stuff is a little funky but I think mostly-reasonable.

Test Plan: Created and edited /w/, /w/pokemon/, etc.
Reviewed By: hsb
Reviewers: hsb, codeblock, jungejason, aran, tuomaspelkonen
CC: aran, hsb
Differential Revision: 643