More detailed account status on billing page.

Also, show account status even if there's no active subscription.

https://www.pivotaltracker.com/story/show/71344322
Added "please check" message to billing form.

https://www.pivotaltracker.com/story/show/73218336
Highlight inactive subscriptions.

These are the ones that used to be "Needs Approval." I highlighted "new"
a lot because it needs attention; "cancelled" and "disabled" are
de-emphasized, which does make them stand out but doesn't demand the
eye.

https://www.pivotaltracker.com/story/show/71344322
Updated be-careful message on billing form.

https://www.pivotaltracker.com/story/show/73218336
Show "please check" message only when updating billing.

For a new subscription with a blank form, the message is somewhat
condescending; of course they're going to try to get it correct.
The purpose of this message is to ask them to pay attention when
we're pre-filling the form with info that may be out of date.

We check `Organization.subscription` rather than
`@subscription.persisted` because under the hood, we may be editing a
new subscription object with info copied from the old one.

https://www.pivotaltracker.com/story/show/73218336
Explain that payment date is out of our control.

https://www.pivotaltracker.com/story/show/71344926