Refactored theme.jsx component from PR [mui#797](mui#797)

Separated out decorator into src/styles/theme-decorator.js so that it no longer relies on another
wrapper component.

Author: Shaurya Arora

src/styles/index.js

@@ -7,4 +7,5 @@ module.exports = {
   Typography: require('./typography'),
   LightRawTheme: require('./raw-themes/light-raw-theme'),
   DarkRawTheme: require('./raw-themes/dark-raw-theme'),
+  ThemeDecorator: require('./theme-decorator'),
 };

src/styles/theme-decorator.js

@@ -0,0 +1,25 @@
+const React = require('react');
+
+module.exports = (customTheme) => {
+
+  return function(Component) {
+
+    return React.createClass({
+
+      childContextTypes : {
+        muiTheme: React.PropTypes.object,
+      },
+
+      getChildContext () {
+        return {
+          muiTheme: customTheme,
+        };
+      },
+
+      render() {
+        return React.createElement(Component, null);
+      },
+    });
+
+  };
+}