Fix context menu being present on rules pages

Fix #32

app.vue

@@ -42,6 +42,11 @@ function keyUpHandler(e: KeyboardEvent) {
   e.preventDefault()
   return false
 }
+
+function contextMenuHandler(e: MouseEvent) {
+  e.preventDefault()
+}
+
 function mouseDownHandler(e: MouseEvent) {
   if (e.button !== 2) { return }
   goStore.zoomKeyPressed = true
@@ -62,12 +67,14 @@ function follow_mouse(e: MouseEvent) {
 }
 
 onMounted(() => {
+  window.addEventListener("contextmenu", contextMenuHandler)
   window.addEventListener("mousedown", mouseDownHandler)
   window.addEventListener("mouseup", mouseUpHandler)
   document.addEventListener("mousemove", follow_mouse)
 })
 
 onUnmounted(() => {
+  window.removeEventListener("contextmenu", contextMenuHandler)
   window.removeEventListener("mousedown", mouseDownHandler)
   window.removeEventListener("mouseup", mouseUpHandler)
   document.removeEventListener("mousemove", follow_mouse)