[timeline] sticky header, scroll to hour....

app/src/plugins/app@vendor/vue-cal/weekdays-headings.vue

@@ -1,6 +1,7 @@
 <template lang="pug">
 //- weekdays-headings are on week view only.
-.vuecal__flex.vuecal__weekdays-headings
+.vuecal__flex.vuecal__weekdays-headings(
+  ref="vuecal_weekday_heading")
   template(v-for="(heading, i) in headings" :key="i")
     .vuecal__flex.vuecal__heading(
       v-if="!heading.hide"
@@ -31,7 +32,8 @@ export default {
     transitionDirection: { type: String, default: 'right' },
     weekDays: { type: Array, default: () => [] },
     switchToNarrowerView: { type: Function, default: () => {} },
-    unscheduledTime: { type: Array, default: [] }
+    unscheduledTime: { type: Array, default: [] },
+    // viewPortOffset: { type: Number, default: 0 },
   },
 
   methods: {
@@ -48,7 +50,10 @@ export default {
       name: heading.name,
       initials: heading.initials,
       ...(heading.today ? { today: heading.today } : {})
-    })
+    }),
+    onTimelineScroll(viewPortOffset) {
+      this.$refs['vuecal_weekday_heading'].style.top = `${viewPortOffset}px`
+    }
   },
 
   computed: {