Remove usermanager

[danirabbit]

Closes elementary/quick-settings#44
Closes #67
Closes #71
Closes #127
Closes #146
Closes #158

Proposing to remove the userlist/quick user switching completely. It seems like this feature only really exists to pre-select an account on the Greeter which seems kind of pointless. In the interest of elementary/wingpanel#446, I'd like to stripe this menu down and start adding in some of the quick settings actions that folks have been asking for

[zeebok]

Code looks good. Should we have some kind of indication of whom is logged currently? Maybe the new logout button could say in the tooltip or something?

[danirabbit]

That's a good question. I mainly opened this hoping to get some feedback from people who maybe use these features, but so far I haven't heard anything 😅

I know @jeremypw and @ryonakano worked on reviewing the PR for this feature so maybe they have opinions about the utility of showing the name of the logged in user?

[TomiOhl]

Should we have some kind of indication of whom is logged currently?

Tbh I liked seeing my username and profile pic there, but never used it to switch users.

[jhaygood86]

My own preference would be to keep displaying current user and profile but remove fast user switching. It's pretty rare for devices to be shared, and logging out and back in is probably acceptable for those devices that are shared

[zeebok]

Likewise, I do like seeing my profile pic and name

[jeremypw]

I do sometimes use user switching when developing in order to try something as a different user without losing the current user set up (which would happen if I logged out), so I would be sorry to see this go.