[Frontend] Form styling

#772
Added ".l-controls-under" styling to allow
channel-selector layout;
Added new hint color constants and refined
style defs;

platform/forms/res/templates/form.html

@@ -33,7 +33,7 @@
                                invalid: mctFormInner.$dirty && !mctFormInner.$valid,
                                first: $index < 1,
                                'l-controls-first': row.layout === 'control-first',
-                               'l-input-sm': row.inputsize === 'sm'
+                               'l-controls-under': row.layout === 'controls-under'
                                }">
                     <div class='label flex-elem' title="{{row.description}}">
                         {{row.name}}