Help people without permissions claim issues

Servo has the wonderful problem of new contributors stepping on each others' toes for introductory bugs. To reduce this, it would be nice to have Highfive note that an issue is claimed when someone claims it. I can think of two ways to implement an "assign to newbie":

• Find or make the "C-Assigned" tag, tag the issue with it, comment "this issue was claimed by ___ on //____"
• Add the new user to a team with read-only permissions, then add them as the actual assignee in the github UI (not sure if this works; it should be documented on https://help.github.com/articles/permission-levels-for-an-organization-repository/ and I've contacted support to get it added)

Either way, I'd propose a syntax like "@highfive assign @username" (usable by people with r+ perms on the repo to assign to arbitrary newbies) plus "@highfive assign me" for someone who has no perms yet to claim the ticket through whichever mechanic we decide.

It could also be nice to have the issue-claiming syntax include a timeout, like "@highfive assign me 1week", and have highfive unassign the issue if it ever sits for longer than the specified timeout with no new comments.

@jdm, thoughts?

The issue names no files, tests, or entry points. Start by resolving whether claiming should use labels/comments or GitHub assignees, then define the command syntax and timeout behavior; done means an agreed implementation path for claiming and releasing issues.