Support replace feature; close #188; multiple bug fixes on upload

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assets/src/components/prompts/Replace.vue

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+<template>
+  <div class="prompt">
+    <h3>{{ $t('prompts.replace') }}</h3>
+    <p>{{ $t('prompts.replaceMessage') }}</p>
+
+    <div>
+      <button class="ok"
+        @click="showConfirm"
+        :aria-label="$t('buttons.replace')"
+        :title="$t('buttons.replace')">{{ $t('buttons.replace') }}</button>
+      <button class="cancel"
+        @click="$store.commit('closeHovers')"
+        :aria-label="$t('buttons.cancel')"
+        :title="$t('buttons.cancel')">{{ $t('buttons.cancel') }}</button>
+    </div>
+  </div>
+</template>
+
+<script>
+import { mapState } from 'vuex'
+
+export default {
+  name: 'replace',
+  computed: mapState(['showConfirm'])
+}
+</script>