* Show the ban length instead of the ban expiration date in ban notices.
* Fix the ban notice to not say "Your account has been temporarily
banned" when it's a permanent ban.
* Remove .ui-corner-all, .ui-state-highlight, .ui-state-error classes
from notice boxes.
* Use .notice, .notice-info, .notice-error classes instead.
* Replace <p> elements in notices with <div>'s so that we don't have to
work around the `margin-bottom: 1em` from <p> elements.
* Replace <h1> elements in notices with <h2>.
* Standardize info notices to use the same shade of light yellow in the
light theme.
Ensure dtext is always wrapped in a `<div class="prose">` or
`<span class="prose">` (for inline dtext) container so that dtext css is
properly applied.
