Add explanatory text to planner's no-data message

lib/www/client/source/src/views/Plan.vue

@@ -37,6 +37,7 @@
         :search="filter"
         :loading="loading"
         :fixed-header="true"
+        no-data-text="No planned lines. Add lines via the context menu from either the Lines or Sequences view."
         :item-class="(item) => (activeItem == item && !edit) ? 'blue accent-1 elevation-3' : ''"
         @click:row="setActiveItem"
         @contextmenu:row="contextMenu"