Refactor contact editor form element templates markup and style

UI/WebServerResources/scss/core/layout.scss

@@ -13,3 +13,6 @@ layout-fill,
 flex, flex-sm, flex-gt-sm, flex-md, flex-gt-md, flex-lg, flex-gt-lg, hide, hide-sm, hide-gt-sm, hide-md, hide-gt-md, hide-lg, hide-gt-lg, show, show-sm, show-gt-sm, show-md, show-gt-md, show-lg, show-gt-lg;
 
 @include attributesToClasses($selectors);
+.md-flex {
+  flex: 1 1 auto;
+}

UI/WebServerResources/scss/core/mixins.scss

@@ -24,7 +24,7 @@
   @each $selector in $selectors {
     .md-#{$selector} {
 // no syntax error here
-      @extend [#{$selector}] !optional
+      @extend #{'['$selector']'} !optional
     }
   }
 }