refactor: svg icons (#1096)

* refactor svg

* add svgo

* refine

* add tree.svg

* add svg.yml

src/views/login/index.vue

@@ -9,7 +9,7 @@
       </div>
 
       <el-form-item prop="username">
-        <span class="svg-container svg-container_login">
+        <span class="svg-container">
           <svg-icon icon-class="user" />
         </span>
         <el-input
@@ -243,9 +243,6 @@ $light_gray:#eee;
     vertical-align: middle;
     width: 30px;
     display: inline-block;
-    &_login {
-      font-size: 20px;
-    }
   }
   .title-container {
     position: relative;