fieldset disabled styles (#1682)

* fieldset disabled styles

* Added disabled styles to button elements included inside a disabled fieldset

* Added comma, and fieldset element reset

* fieldset doesn't need display block

sass/base/generic.sass

@@ -103,6 +103,9 @@ strong
 
 // Block
 
+fieldset
+  border: none
+
 pre
   +overflow-touch
   background-color: $pre-background