Remove show/hide behaviour from permissions form

In research we found that:
- people didn’t initially realise that the permissions expanded when the
  ‘admin’ option was selected
- not having all the options visible at once makes it hard to know what
  permissions you are (and more importantly aren’t) giving to people

This commit makes it so that:
- the options within the ‘admin’ option are always visible
- a bit of Javascript logic makes it so you can pick ‘caseworker’ and
  ‘manage service’, for example (by deselecting one when you pick the
  other)

app/assets/stylesheets/components/conditional-radios.scss

@@ -1,4 +1,5 @@
 $border-thickness: 9px;
+$top-spacing: $gutter + 5px;
 
 .multiple-choice {
 
@@ -6,7 +7,7 @@ $border-thickness: 9px;
 
   .block-label {
     &:before {
-      box-shadow: 0 4px 0 0 $white;
+      box-shadow: 0 5px 0 0 $white;
     }
   }
 
@@ -16,10 +17,10 @@ $border-thickness: 9px;
 
   &-panel {
     border-left: $border-thickness solid $border-colour;
-    margin: 0 0 0 ($border-thickness + 6px);
-    padding: $gutter-one-third 0 0 ($gutter - 3px);
+    margin: 0 0 (-$top-spacing - $gutter) $gutter-half;
+    padding: $top-spacing 0 0 ($gutter - 3px);
     position: relative;
-    top: -$gutter-one-third;
+    top: -$top-spacing;
     z-index: 1;
   }