More safeguards, some fixes, standardized some code, WireGuard update script, removed redundant code

- Add curl as a dependency for those who run the script without 'curl URL | bash'.
  - Use POSIX 'command -v' instead of 'hash'.
  - Check if packages have actually been installed and abort execution if they have not.
  - Fixed issue with getStaticIPv4Settings() that prevented existing network settings
    to be used as static IP settings when running the script unattended with empty
    $IPv4addr and $IPv4gw variables.
  - Exit if processing wireguard-linux-compat fails.
  - Exit if 50unattended-upgrades fails to extract.
  - Exit clientSTAT.sh if the wg0 interface is not available.
  - Moved the Self Check to a single script since dedicated versions were very similar.
  - Add 'pivpn -wg' to update WireGuard for users running Raspbian with armv6l kernel.

scripts/wireguard/pivpn

@@ -54,6 +54,11 @@ updateScripts(){
     exit 0
 }
 
+updateWireGuard(){
+    $SUDO /opt/pivpn/wgUPDATE.sh
+    exit 0
+}
+
 backup(){
   $SUDO /opt/pivpn/backup.sh
 }
@@ -73,7 +78,8 @@ showHelp(){
     echo ":::  -h,  help             Show this help dialog"
     echo ":::  -u,  uninstall        Uninstall pivpn from your system!"
     echo ":::  -up, update           Updates PiVPN Scripts"
-    echo ":::  -bk, Backup           Backup vpn configs and user profiles"
+    echo ":::  -wg, wgupdate         Updates WireGuard"
+    echo ":::  -bk, backup           Backup VPN configs and user profiles"
     exit 0
 }
 
@@ -92,6 +98,7 @@ case "$1" in
 "-h"  | "help"               ) showHelp;;
 "-u"  | "uninstall"          ) uninstallServer;;
 "-up" | "update"             ) updateScripts "$@" ;;
+"-wg" | "wgupdate"           ) updateWireGuard ;;
 "-bk" | "backup"             ) backup ;;
 *                            ) showHelp;;
 esac