Add Vue.js slot support

[i906]

Adding slots allows certain HTML blocks to be overwritten.

Usage without slots

<vue-snotify :class="style"></vue-snotify>

Available slots

• progressBar
• inner
• title
• body
• prompt
• icon
• buttons

Usage to override icon

<vue-snotify :class="style">
  <template slot="toast" slot-scope="{snotify}">
    <toast :toastData="snotify.toast" :key="snotify.toast.id" @stateChanged="snotify.stateChanged">
      <div class="icon" slot="icon" slot-scope="{toast}">
        <span class="w-48 rounded accent">
          <i class="material-icons" v-if="toast.config.type === 'success'">&#xE24B;</i>
        </span>
      </div>
    </toast>
  </template>
</vue-snotify>

Usage to allow HTML in body or title

<vue-snotify :class="style">
  <template slot="toast" slot-scope="{snotify}">
    <toast :toastData="snotify.toast" :key="snotify.toast.id" @stateChanged="snotify.stateChanged">
      <template slot="title" slot-scope="{toast}">
        <div class="snotifyToast__title" v-html="toast.title"></div>
      </template>
      <template slot="body" slot-scope="{toast}">
        <div class="snotifyToast__body" v-html="toast.body"></div>
      </template>
    </toast>
  </template>
</vue-snotify>