[VBIV-8878] Confirmation on Mark Forums Read

In the navbar template, adding a simple JavaScript confirmation dialog when someone clicks on "Mark Forums Read" would be huge. I can't even count the number of times users have cried because they accidentally clicked it.

This:

<a href="forumdisplay.php?{vb:raw session.sessionurl}do=markread&amp;markreadhash={vb:raw bbuserinfo.securitytoken}">{vb:rawphrase mark_forums_read}</a>

Could instead be this:

<a href="forumdisplay.php?{vb:raw session.sessionurl}do=markread&amp;markreadhash={vb:raw bbuserinfo.securitytoken}" onclick="return confirm('{vb:rawphrase mark_forums_read_confirm}')">{vb:rawphrase mark_forums_read}</a>

The Unable to render embedded object: File (mark_forums_read_confirm) not found. phrase could be something along these lines: Are you sure you want to mark the entire forum as being read? There is no undo.