Auto select one and only cluster from pasted config (#888)

* Auto select one and only cluster from pasted config

- Disable add button with tooltip if no clusters are selected
- Add functionality to tooltip to display correctly over disabled
  elements

* feature should work of any method of adding kube config

Signed-off-by: Sebastian Malton <sebastian@malton.name>
Co-authored-by: Sebastian Malton <smalton@mirantis.com>

src/renderer/components/button/button.scss

@@ -54,8 +54,7 @@
 
   form:not([novalidate]):invalid &[type=submit]:not(.active),
   &:disabled {
-    color: silver;
-    background: $buttonDisabledBackground;
+    opacity: 50%;
     pointer-events: none;
   }
 
@@ -112,4 +111,4 @@
     left: 100%;
     width: 0;
   }
-}
+}