Lazy-load emoji picker in post form

When clicking the reply button, we used to load the whole emoji picker.
This causes a considerable delay even if the user is not going to use
the emoji picker. Now the content of the emoji picker is loaded only
after the user has explicitly opened the emoji picker.

Ref: grouped-emoji-picker

src/components/emoji_input/emoji_input.vue

@@ -19,6 +19,7 @@
         v-if="enableEmojiPicker"
         ref="picker"
         :class="{ hide: !showPicker }"
+        :showing="showPicker"
         :enable-sticker-picker="enableStickerPicker"
         class="emoji-picker-panel"
         @emoji="insert"

src/components/emoji_picker/emoji_picker.js

@@ -38,6 +38,10 @@ const EmojiPicker = {
       required: false,
       type: Boolean,
       default: false
+    },
+    showing: {
+      required: true,
+      type: Boolean
     }
   },
   data () {
@@ -47,7 +51,9 @@ const EmojiPicker = {
       showingStickers: false,
       groupsScrolledClass: 'scrolled-top',
       keepOpen: false,
-      customEmojiTimeout: null
+      customEmojiTimeout: null,
+      // Lazy-load only after the first time `showing` becomes true.
+      contentLoaded: false
     }
   },
   components: {
@@ -114,6 +120,9 @@ const EmojiPicker = {
       this.$lozad = lozad('img', {})
       this.$lozad.observe()
     },
+    waitForDomAndInitializeLazyLoad() {
+      this.$nextTick(() => this.initializeLazyLoad())
+    },
     destroyLazyLoad () {
       if (this.$lozad) {
         if (this.$lozad.observer) {
@@ -128,18 +137,23 @@ const EmojiPicker = {
   watch: {
     keyword () {
       this.onScroll()
-      // Wait for the dom to change
-      this.$nextTick(() => this.initializeLazyLoad())
+      this.waitForDomAndInitializeLazyLoad()
     },
     allCustomGroups () {
-      this.$nextTick(() => this.initializeLazyLoad())
+      this.waitForDomAndInitializeLazyLoad()
+    },
+    showing (val) {
+      if (val) {
+        this.contentLoaded = true
+        this.waitForDomAndInitializeLazyLoad()
+      }
     }
   },
   mounted () {
     if (this.defaultGroup) {
       this.highlight(this.defaultGroup)
     }
-    this.initializeLazyLoad()
+    this.waitForDomAndInitializeLazyLoad()
   },
   destroyed () {
     this.destroyLazyLoad()

src/components/emoji_picker/emoji_picker.vue

@@ -1,5 +1,7 @@
 <template>
-  <div class="emoji-picker panel panel-default panel-body">
+  <div
+    class="emoji-picker panel panel-default panel-body"
+  >
     <div class="heading">
       <span class="emoji-tabs">
         <span
@@ -45,7 +47,10 @@
         </span>
       </span>
     </div>
-    <div class="content">
+    <div
+      v-if="contentLoaded"
+      class="content"
+    >
       <div
         class="emoji-content"
         :class="{hidden: showingStickers}"