合并dev,修复冲突，修改比赛列表中的小bug

template/src/oj/contest/contest_problem.html

@@ -8,9 +8,6 @@
         <li role="presentation"><a
                 href="/contest/{{ contest_problem.contest.id }}/problem/{{ contest_problem.id }}/submissions/">我的提交</a>
         </li>
-        <li role="presentation"><a
-                href="/contest/{{ contest_problem.contest.id }}/problems/">返回</a>
-        </li>
     </ul>
     <h2 class="text-center">{{ contest_problem.title }}</h2>
 
@@ -40,6 +37,7 @@
             {% for item in samples %}
                 <div class="problem-section">
                     <label class="problem-label">样例输入{{ forloop.counter }}</label>
+                    <a href="javascript:void(0)" class="copy-sample" data-clipboard-text="{{ item.input }}">复制</a>
         <pre>
 {{ item.input }}</pre>