Move dropzone.js to npm/webpack

- unvendor dropzone and upgrade it from 4.2.0 to 5.7.0
- make `csrf` available on window.config

package.json

@@ -7,6 +7,7 @@
  "dependencies": {
  "@primer/octicons": "9.4.0",
  "clipboard": "2.0.4",
+ "dropzone": "5.7.0",
  "fomantic-ui": "2.8.4",
  "highlight.js": "9.18.1",
  "jquery": "3.4.1",

public/vendor/librejs.html

@@ -61,9 +61,9 @@
  <td><a href="https://github.com/Ranks/emojify.js/archive/1.1.0.tar.gz">emojify-1.1.0.tar.gz</a></td>
  </tr>
  <tr>
- <td><a href="./plugins/dropzone/dropzone.js">dropzone.js</a></td>
- <td><a href="https://github.com/enyo/dropzone/blob/master/LICENSE">Expat</a></td>
- <td><a href="https://github.com/enyo/dropzone/archive/v4.2.0.tar.gz">dropzone.js-4.2.0.tar.gz</a></td>
+ <td><a href="./js/dropzone.js">dropzone.js</a></td>
+ <td><a href="https://github.com/enyo/dropzone/blob/master/LICENSE">MIT</a></td>
+ <td><a href="https://github.com/enyo/dropzone/archive/master.tar.gz">dropzone-master.tar.gz</a></td>
  </tr>
  <tr>
  <td><a href="./highlight.js">highlight.js</a></td>