Add expiration date and delete button to UI for API tokens

[scolapasta]

On the API token tab of the user page, add the expiration date of the token and a button to delete the exisiting token (currently only have a regenerate token button).

This would match the API logic introduced in #6266

[TaniaSchlatter]

Quick mockup from our discussion, showing what needs to be added to the existing UI:

[mheppler]

Cleaned up api token experation date layout on api token tab of account pg.

(NOTE: Screenshot updated using Kevin's QA build, as my original screenshot in this comment was not made with the latest and greatest code changes.)

[TaniaSchlatter]

If the time is hard coded to a year, let's:
a) add a few words of text to the page:
"Your API Token is displayed below after it has been created, and is valid for a year. Checkout our API guide..."

b) add an "Expired" message:

Thanks for catching, @kcondon and for mock ups, @mheppler

[mheppler]

Added api token expiration warning and error msgs to bundle and xhtml, needs backend render logic. Passing to @sekmiller.

[sekmiller]

@TaniaSchlatter, @mheppler what is our definition of "about to expire"?

[TaniaSchlatter]

I don't think we need the warning in the UI. Users will have the date and timeframe in front of them to provide the info needed. That's why I didn't include it in the note above.