updating icons for settings and filters

include/class.nav.php

scp/css/scp.css

scp/images/icons/alert-settings.gif

scp/images/icons/email-autoresponders.gif

scp/images/icons/email-settings.gif

scp/images/icons/kb-settings.gif

scp/images/icons/new_ticket_filter.png

scp/images/icons/ticket-settings.gif

scp/images/icons/ticket_filters.png

scp/images/icons/ticket_source_other.png