feat: made fullscreen button depend on images

vue-theme/src/pages/single.vue

     article.f-grow.shadow
         header
             h1 {{ type }}:{{ $route.params.slug }} single
-            button(@click="fullscreengallery = true") fullscreen
+            button(v-if="images.length > 0" @click="fullscreengallery = true") fullscreen
         section(v-if="posts[$route.params.slug]")
             h4 {{ posts[$route.params.slug].title }}
             .block-wrapper(v-for="block in posts[$route.params.slug].blocks" v-html="block")