Updated AP_Clear_cache.php

Since forum version 1.4 has the ranks cache and 1.5 does not we do not
show the button
Updated AP_Broadcast_Email.php
Updated plugins to have class="plugin" and

Added the generate_admin_menu( $plugin ); just before the message so we
can see the menu.
Updated clear_cache to check for for version diff via version_compare()
Merge pull request #3 from kierownik/master

Canged the files a bit