Make Filter icon smaller to look better a side of Search icon

https://github.com/FortAwesome/Font-Awesome/issues/11873

skins/elastic/styles/layout.less

@@ -202,6 +202,10 @@ html.iframe {
             margin: 0;
             width: 1.4em;
         }
+
+        a.button.filter:before {
+            font-size: 1.6rem; // this icon is too big in FA5
+        }
     }
 
     body > #layout > div > .header {

skins/elastic/styles/widgets/buttons.less

@@ -52,6 +52,7 @@ button.btn {
     }
     &.filter:before {
         content: @fa-var-filter;
+        font-size: 1.2em; // this icon is too-big in FA5
     }
     &.import:before {
         content: @fa-var-upload;