Add email loading state until user info resolved

[deckar01]

Expose a function in session that returns a promise that resolves to the user private info.
Add a loading state and an error state to the email setting.

Fixes #1059.

[bartekn]

Pulled & tested 👍

[thejollyrogers]

Here's an idea:
instead of creating new promise waitingForUserInfo and creating a new method (we already have a method getUser() in session), make User.load return a promise and store it in the session cache.

session.js line 88 do:

cache.set("userPrivateInfo", UserPrivateInfo.load...)

then just call getUser() inside email settings, and it will return either the unresolved promise or the user object.

[deckar01]

@thejollyrogers I agree that is how it should have been designed in the first place, but I don't want to change getUser(), because I would have to change all 108 usages which would significantly increase the surface area of this PR.

[thejollyrogers]

if we're taking the time to fix it now, shouldn't we take the time to do it right rather than moving forward with redundancy, different implementations, and confusion?

[deckar01]

@thejollyrogers This PR is to fix #1059, not refactor the way the entire app waits for user data. Opened issue #1129 to unify the code paths.

[thejollyrogers]

Okay, thank you