Prompt on `app .. config` if $EDITOR is un-set

Closes #41

abra

@@ -684,6 +684,31 @@ sub_app_undeploy (){
 sub_app_config (){
   load_instance
 
+  if [ -z "$EDITOR" ]; then
+    warning "\$EDITOR not set; which text editor would you like to use?"
+
+    EDITORS_ALL=(vi vim nano pico emacs)
+    declare -a EDITORS_AVAILABLE
+
+    for EDITOR in "${EDITORS_ALL[@]}"; do
+      if type "$EDITOR" > /dev/null 2>&1; then
+        EDITORS_AVAILABLE+=("$EDITOR")
+      fi
+    done
+
+    if [ ${#EDITORS_AVAILABLE[@]} = 0 ]; then
+      error "No text editors found! Are you using a magnetised needle? 🤪"
+    fi
+
+    select EDITOR in "${EDITORS_AVAILABLE[@]}"; do
+      if [ 1 -le "$REPLY" ] && [ "$REPLY" -le ${#EDITORS_AVAILABLE[@]} ]; then
+        SERVER="$EDITOR"
+        success "Using '${EDITOR}'; Add 'export EDITOR=${EDITOR}' to your ~/.bashrc to set as default"
+        break
+      fi
+    done
+  fi
+
   $EDITOR "$ENV_FILE"
 }