Fix task hovercards showing a "Not Editable" state

Summary:
Ref T13269. These cards really have three states:

• Editable: shows a pencil icon edit button.
• You Do Not Have Permission To Edit This: shows a "no editing" icon in red.
• Hovecard: shouldn't show anything.

However, the "hovercard" and "no permission" states are currently the same state, so when I made the "no permission" state more obvious that made the hovercard go all weird.

Make these states explicitly separate states.

Test Plan:
Looked at a...

• Editable card on workboard: edit state.
• No permission card on workboard: no permission state.
• Any hovercard: "not editable, this is a hovercard" state.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13269

Differential Revision: https://secure.phabricator.com/D20330