Allow installer to specify own DNS servers

Offers "other" option.
Gives Installer chance to review settings before continuing.

automated install/basic-install.sh

@@ -286,9 +286,10 @@ setStaticIPv4() {
 }
 
 setDNS(){
-	DNSChoseCmd=(whiptail --separate-output --radiolist "Select Upstream DNS Provider" $r $c 2)
+	DNSChoseCmd=(whiptail --separate-output --radiolist "Select Upstream DNS Provider" $r $c 3)
 	DNSChooseOptions=(Google "" on
-					  OpenDNS "" off)
+					  OpenDNS "" off
+					  Other "" off)
 	DNSchoices=$("${DNSChoseCmd[@]}" "${DNSChooseOptions[@]}" 2>&1 >/dev/tty)
 	if [[ $? = 0 ]];then
 		case $DNSchoices in
@@ -302,6 +303,23 @@ setDNS(){
 				piholeDNS1="208.67.222.222"
 				piholeDNS2="208.67.220.220"
 				;;
+            Other)
+                until [[ $DNSSettingsCorrect = True ]]
+                do
+                    piholeDNS=$(whiptail --backtitle "Specify Upstream DNS Provider(s)"  --inputbox "Enter your desired upstream DNS provider(s)" $r $c "8.8.8.8, 8.8.4.4" 3>&1 1>&2 2>&3)
+                    piholeDNS1=$(echo $piholeDNS | sed 's/[, \t]\+/,/g' | awk -F, '{print$1}')
+                    piholeDNS2=$(echo $piholeDNS | sed 's/[, \t]\+/,/g' | awk -F, '{print$2}')
+
+                    if (whiptail --backtitle "Specify Upstream DNS Provider(s)" --title "Upstream DNS Provider(s)" --yesno "Are these settings correct?
+							DNS Server 1:   $piholeDNS1
+                            DNS Server 2:   $piholeDNS2" $r $c) then
+							DNSSettingsCorrect=True
+					else
+						# If the settings are wrong, the loop continues
+						DNSSettingsCorrect=False
+					fi
+                done
+                ;;
 		esac
 	else
 		echo "::: Cancel selected. Exiting..."
@@ -342,8 +360,16 @@ versionCheckDNSmasq(){
   $SUDO cp $newFileToInstall $newFileFinalLocation
   echo " done."
   $SUDO sed -i "s/@INT@/$piholeInterface/" $newFileFinalLocation
-  $SUDO sed -i "s/@DNS1@/$piholeDNS1/" $newFileFinalLocation
-  $SUDO sed -i "s/@DNS2@/$piholeDNS2/" $newFileFinalLocation
+  if [[ "$piholDNS1" != "" ]]; then
+    $SUDO sed -i "s/@DNS1@/$piholeDNS1/" $newFileFinalLocation
+  else
+    $SUDO sed -i '/^server=@DNS1@/d' $newFileFinalLocation
+  fi
+  if [[ "$piholDNS2" != "" ]]; then
+    $SUDO sed -i "s/@DNS2@/$piholeDNS2/" $newFileFinalLocation
+  else
+    $SUDO sed -i '/^server=@DNS2@/d' $newFileFinalLocation
+  fi
 }
 
 installScripts() {