ImagePicker: introduce 'mode' - simple/editable

We have two cases for the picker:
* in normal pages: here the image upload/reset happens automatically. this is
  the editable mode with action buttons.

* in dialogs: here you just upload images . this is simple mode.

dashboard/src/components/app/Display.vue

@@ -97,7 +97,7 @@ onMounted(() => {
   <div>
     <div style="display: inline-block;">
       <label>{{ $t('app.display.icon') }}</label>
-      <ImagePicker ref="imagePicker" :src="iconUrl" fallback-src="/img/appicon_fallback.png" :save-handler="onIconSubmit" :unset-handler="onIconUnset" :size="512" display-height="128px"/>
+      <ImagePicker ref="imagePicker" mode="editable" :src="iconUrl" fallback-src="/img/appicon_fallback.png" :save-handler="onIconSubmit" :unset-handler="onIconUnset" :size="512" display-height="128px"/>
     </div>
 
     <form @submit.prevent="onSubmit()" autocomplete="off">