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/update.sh

@@ -15,6 +15,17 @@ fi
 
 source "${setupVars}"
 
+scriptusage(){
+    echo "::: Updates PiVPN scripts"
+    echo ":::"
+    echo "::: Usage: pivpn <-up|update> [-t|--test]"
+    echo ":::"
+    echo "::: Commands:"
+    echo ":::  [none]              Updates from master branch"
+    echo ":::  -t, test            Updates from test branch"
+    echo ":::  -h, help            Show this usage dialog"
+}
+
 ###Functions
 ##Updates scripts
 updatepivpnscripts(){
@@ -68,14 +79,6 @@ cloneupdttest(){
   git -C "$pivpnlocalpath" checkout master
 }
 
-scriptusage(){
-    echo -e "Updates pivpn scripts,
-
-              Usage:
-              pivpn update              | updates from master branch
-              pivpn update -t or --test | updates from test branch"
-}
-
 ## SCRIPT
 
 if [[ $# -eq 0 ]]; then
@@ -83,15 +86,15 @@ if [[ $# -eq 0 ]]; then
 else
   while true; do
     case "$1" in
-      -t|--test|test)
+      -t|test)
           updatefromtest
           exit 0
           ;;
-      -h|--help|help)
+      -h|help)
           scriptusage
           exit 0
           ;;
-      * )
+      *)
         updatepivpnscripts
         exit 0
         ;;