Fix unbound shortcut links

Fixes redmine #4151
1) Make the naming in shortcuts.inc more clear - forwarder=dnsmasq
resolver=unbound
2) Make the value of $shortcuts_section correct in each dnsmasq and
unbound php code
3) Make diag_logs_resolver.php smarter, so if dnsmasq is enabled, then
show shortcuts for dnsmasq, otherwise show shortcuts for unbound.
4) Fix some references to forwarder in unbound code - should be
resolver.