Follow-up from "feat: fab with highlight all/none"

The following discussion from !168 (merged) should be addressed:

• @schneider210 started a discussion: (+1 comment)

  I'd like to suggest to split our template: e.g. having a single component for the list, another one for the highlight buttons and an additional one for the (upcoming) anno-type toggles to keep the code leaner and maintainable this time. If you agree, I could turn it into a mixin along with the data needed herefore.

  So this suggestion applies to the following lines as well dealing with the buttons.

  Our complete template could finally look sth like this:

  <template>
    <div
      v-if="annotations.length"
      class="q-ma-sm annotations"
    >
      <AnnotationTypes />
  
      <AnnotationList />
  
      <AnnotationOptions />
    </div>
  
    <div
      v-else
      class="q-pa-sm"
    >
      <Notification :message="$t(messages.none)" />
    </div>
  </template>