Better layout for mutlidselect

- use full width
- center icon

Fixes #919
Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/static/style-bootstrap.css

@@ -244,11 +244,13 @@ img.engage-icon {
 }
 .ms-container{
   background: none !important;
+  width: 100%;
 }
 .fa-multiselect {
   height: 200px;
   line-height: 200px;
   float: left;
   vertical-align: middle;
-  padding-left: 10px;
+  width: 10%;
+  text-align: center;
 }