feat(user): fully support the Visible Role field

[wescopeland]

This PR adds full support for the Visible Role field in a user's settings. A migration has been included which adds a UserAccounts.visible_role_id field.

How it works:
Given a user has 2 or more roles attached, they may select which one is publicly visible from their settings:

Once a visible_role_id is set, it is respected on the user profile, forum author box, and user card tooltips:

Implementation details:
The meat of this PR is ActsAsCommunityMember::getVisibleRoleAttribute().

visible_role_id is nullable. By default, getVisibleRoleAttribute() is going to return the user's first display-ordered role. For the great majority of folks who have roles, this will either be their Developer or Junior Developer roles.

If the user has a defined visible_role_id value, but they've since lost the role, then the attribute falls back to the first display-ordered role they have attached, or just null.

We'll obviously need to do some kind of mass assignment of team roles after deploy. I can figure out those details later.

[Jamiras]

I also believe we should set the Administrator role to visible

I'm not convinced of that. How would we describe the Administrator role to users? Administrator is similar to Root. It's a super user with access to pretty much anything, while not really being a News Manager, or Event Manager, etc.

Conversely, my roles right now are all hidden except Developer. People know I have more power than that, but Administrator is more of a Title than a Role.

As a user, when would I want to message an Administrator over someone with a more dedicated role?

[wescopeland]

Good point - probably never.

I'm pretty sure each admin should have more specific roles under the current role offerings we have. For example, you and I (and anyone else with write access to our GitHub org) should probably have the "Engineer" role.