separate reply button to its own component, add changelog entry

src/components/reply_button/reply_button.vue

@@ -0,0 +1,21 @@
+<template>
+  <div>
+    <i
+      v-if="loggedIn"
+      class="button-icon button-reply icon-reply"
+      :title="$t('tool_tip.reply')"
+      :class="{'-active': replying}"
+      @click.prevent="$emit('toggle')"
+    />
+    <i
+      v-else
+      class="button-icon button-reply -disabled icon-reply"
+      :title="$t('tool_tip.reply')"
+    />
+    <span v-if="status.replies_count > 0">
+      {{ status.replies_count }}
+    </span>
+  </div>
+</template>
+
+<script src="./reply_button.js"></script>