Clean up ACP attachment management page

The ACP attachment management page should follow the same design as the ACP logs page. Issues:

• The top pagination touches the table.
• The reset & submit buttons are positioned to the left of the pagination. The submit button should simply state "Delete marked" as that is the only action that can be taken.
• The Mark/Unmark links are a row in the table itself. Should appear below "Delete marked" instead.
• If there are no attachments found, there should be a message indicating that.
• When the attachment stats are incorrect, there is a message indicating so at the top of the page. Then there's a separate section in the form below the attachments list with a button to resync the stats. The message at the top should simply have a link to resync the stats instead.