Headings subtitle fix (#31)

Fix Heading classNames mess #29

* removed the htmlFor prop on labels to allow nested label > input without an explicit htmlFor. fixes #27

* changed heading behaviour adding title and subtitle classes at same time. fixes #29

* Revert "removed the htmlFor prop on labels to allow nested label > input without an explicit htmlFor. fixes #27"

This reverts commit e6030c5.

src/components/heading/__test__/__snapshots__/heading.test.js.snap

@@ -11,7 +11,7 @@ exports[`Heading component Should be a subtitle with size rendered as P 1`] = `
 
 exports[`Heading component Should be spaced 1`] = `
 <p
-  className="title subtitle is-spaced"
+  className="title is-spaced"
   style={Object {}}
 >
   Subtitle
@@ -20,7 +20,7 @@ exports[`Heading component Should be spaced 1`] = `
 
 exports[`Heading component Should concat classname in props with Bulma classname 1`] = `
 <h1
-  className="other-class this-is-a-test title subtitle"
+  className="other-class this-is-a-test title"
   style={Object {}}
 >
   <p>
@@ -33,7 +33,7 @@ exports[`Heading component Should exist 1`] = `[Function]`;
 
 exports[`Heading component Should have title classname 1`] = `
 <h1
-  className="title subtitle"
+  className="title"
   style={Object {}}
 >
   Test 
@@ -54,7 +54,7 @@ exports[`Heading component Should not be spaced because is subtitle 1`] = `
 
 exports[`Heading component Should use inline styles 1`] = `
 <h1
-  className="title subtitle"
+  className="title"
   style={
     Object {
       "height": 250,

src/components/heading/heading.js

@@ -43,7 +43,7 @@ export default class Heading extends PureComponent {
         {...props}
         className={classnames(className, {
           title: !subtitle && !heading,
-          subtitle: !heading,
+          subtitle,
           heading,
           [`is-${size}`]: size,
           'is-spaced': spaced && !subtitle,