Translate 'staff' to 'agent'

bootstrap.php

include/ajax.content.php

include/ajax.reports.php

include/class.auth.php

include/class.email.php

include/class.export.php

include/class.nav.php

include/class.organization.php

include/class.staff.php

include/class.template.php

include/class.ticket.php

include/staff/directory.inc.php

include/staff/filter.inc.php

include/staff/group.inc.php

include/staff/groups.inc.php

include/staff/header.inc.php

include/staff/helptopic.inc.php

include/staff/login.header.php

include/staff/pwreset.login.php

include/staff/pwreset.php