API: Use a standard edit token

Server-side, the code now just checks using the default "salt", which
is an empty string.

Client-side, this eliminates a GET request every time a user wishes to
take an action, and now uses api.postWithToken which automatically
caches tokens and handles badtoken errors.

Bug: 55846
Change-Id: Id61a457f6f4f74ef974f14382df830791aad5e17
Merge "API: Use a standard edit token"