Improve Meteor.user() and .userId()

[lorensr]

I like Meteor.user(userId, fields) and Meteor.userId() work also inside the publish endpoint functions from https://github.com/peerlibrary/meteor-user-extra

Meteor.user() might be the largest culprit for reactivity bugs, and having userId work in pubs would simplify the api – I imagine that error you get when you try Meteor.userId() currently in publishers is pretty common.

Profile writability would be breaking: #3618 (comment)

Obviously it doesn't pass this test:

But I think there should be some exceptions to that rule ☺️

[mitar]

I must say that this my package surprises me again and again. :-) Because Meteor.userId() just works on the server. It is so easy to write code now which can run everywhere.

Also, I think that Blaze needs currentUserId besides just currentUser helper. Because often you just want to check if user is logged in, and not create dependency on the whole document.

[hwillson]

To help provide a more clear separation between feature requests and bugs, and to help clean up the feature request backlog, Meteor feature requests are now being managed under the https://github.com/meteor/meteor-feature-requests repository.

Migrated to meteor/meteor-feature-requests#82.