added drag'n'drop button to project tasks

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

frontend/src/routes/task/ListTask.svelte

@@ -150,6 +150,7 @@
     {#if task.estimated_time}
     <span class="estimated_time">({+task.estimated_time}&nbsp;h)</span>
     {/if}
+    <button class="symbol" title={t('drag_n_drop')}></button>
     {#if states[task.status] != 'PENDING'}
     <button class="symbol" title={t('postpone')} onclick={() => patchTask(map_state('PENDING'))}></button>
     {/if}