Use standalone draft-js-prism-plugin

The Prism plugin @ngs wrote in this repo works great, I wanted to use it
too so I took it
and made it it's own standalone package:
[`draft-js-prism-plugin`](https://github.com/withspectrum/draft-js-prism-plugin)

This PR just deletes your implementation and replaces it with an import
from `draft-js-prism-plugin`. Since the standalone package is basically
just a copy & paste this works just as well as before.

Author: mxstbr

demo/client/components/DemoEditor/index.js

@@ -9,8 +9,23 @@ import Draft, {
   EditorState,
 } from 'draft-js';
 import styles from './styles.css';
-import prismPlugin from '../../plugins/prism';
-
+import Prism from 'prismjs';
+import 'prismjs/components/prism-java';
+import 'prismjs/components/prism-scala';
+import 'prismjs/components/prism-go';
+import 'prismjs/components/prism-sql';
+import 'prismjs/components/prism-bash';
+import 'prismjs/components/prism-c';
+import 'prismjs/components/prism-cpp';
+import 'prismjs/components/prism-kotlin';
+import 'prismjs/components/prism-perl';
+import 'prismjs/components/prism-ruby';
+import 'prismjs/components/prism-swift';
+import createPrismPlugin from 'draft-js-prism-plugin';
+const prismPlugin = createPrismPlugin({
+  prism: Prism,
+});
+console.log(prismPlugin)
 window.Draft = Draft;
 
 const plugins = [

demo/client/plugins/prism.js

@@ -110,6 +110,7 @@
     "decorate-component-with-props": "^1.0.2",
     "draft-js": "~0.10.1",
     "draft-js-checkable-list-item": "^2.0.5",
+    "draft-js-prism-plugin": "^0.1.1",
     "immutable": "~3.7.4"
   }
 }