Fix content overflow in user hovercards

Summary:
Fixes T13273. This element is a bit weird, but I think I fixed it without breaking anything.

The CSS is used by project hovercards and user hovercards, but they each have a class which builds mostly-shared-but-not-really-identical CSS, instead of having a single View class with modes. So I'm not 100% sure I didn't break something obscure, but I couldn't find anything this breaks.

The major issue is that all the text content has "position: absolute". Instead, make the image "absolute" and the text actual positioned content. Then fix all the margins/padding/spacing/layout and add overflow. Seems to work?

Plus: hide availability for disabled users, for consistency with D20342.

Test Plan:
Before:

{F6320155}

After:

{F6320156}

I think this is pixel-exact except for the overflow behavior.

Also:

• Viewed some other user hovercards, including a disabled user. They all looked unchanged.
• Viewed some project hovercards. They all looked good, too.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13273

Differential Revision: https://secure.phabricator.com/D20344