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/UserDialog.vue

@@ -239,7 +239,7 @@ defineExpose({
 
         <div style="display: flex; gap: 20px">
           <div style="width: 80px;">
-            <ImagePicker :src="avatarUrl" fallback-src="/img/avatar-default-symbolic.svg" :size="512" :save-handler="onAvatarSet" display-width="80px"/>
+            <ImagePicker mode="simple" :src="avatarUrl" fallback-src="/img/avatar-default-symbolic.svg" :size="512" :save-handler="onAvatarSet" display-width="80px"/>
           </div>
 
           <FormGroup style="flex-grow: 1">