Slate editor (#38)

* WIP: Slate editor

* WIP

* Focus at start / end working

* ah ha

* Super basic floating toolbar

* Nested list editing

* Pulling more logic into plugins

* inline code markdown

* Backspace at end of code block should remove mark

* Ensure there is always an empty line at editor end

* Add keyboard shortcuts for bold, italic, underline

* Add strikethrough shortcode and toolbar

* Toolbar to declarative
Fixed paragraph styling
Removed unused stuffs

* Super basic link editing

* Split Toolbar, now possible to edit and remove links

* Add new link to selection from toolbar working

* Ensure toolbar doesn't extend off screen

* Fix minor js issues, disable formatting of document title

* Boom, icons

* Remove codemirror, fix MD parsing issues

* CMD+S now saves inplace

* Add --- shortcut for horizontal rule

* Improved styling for link editor

* Add header anchors in readOnly

* More readable core text color

* Restored image file uploading 🎉

* Add support for inline md syntax, ** __ etc

* Centered

* Flooooow

* Checklist support

* Upgrade edit list plugin

* Finally. Allow keydown within rich textarea

* Update Markdown serializer

* Cleanup, remove async editor loading

* Editor > MarkdownEditor
Fixed unsaved changes warning triggered when all changes are saved

* MOAR typing

* Combine edit and view

* Fixed checkboxes still editable in readOnly

* wip

* Breadcrumb
Restored scroll

* Move document scene actions to menu

* Added: Support for code blocks, syntax highlighting

* Cleanup

*  > styled component

* Prevent CMD+Enter from adding linebreak

* Show image uploading in layout activity indicator

* Upgrade editor deps

* Improve link toolbar. Only one scenario where it's not working now

frontend/utils/uploadFile.js

@@ -0,0 +1,44 @@
+// @flow
+import { client } from './ApiClient';
+import invariant from 'invariant';
+
+type File = {
+  blob: boolean,
+  type: string,
+  size: number,
+  name: string,
+  file: string,
+};
+
+export default async function uploadFile(file: File) {
+  const response = await client.post('/user.s3Upload', {
+    kind: file.type,
+    size: file.size,
+    filename: file.name,
+  });
+
+  invariant(response, 'Response should be available');
+
+  const data = response.data;
+  const asset = data.asset;
+  const formData = new FormData();
+
+  for (const key in data.form) {
+    formData.append(key, data.form[key]);
+  }
+
+  if (file.blob) {
+    formData.append('file', file.file);
+  } else {
+    // $FlowFixMe
+    formData.append('file', file);
+  }
+
+  const options: Object = {
+    method: 'post',
+    body: formData,
+  };
+  await fetch(data.uploadUrl, options);
+
+  return asset;
+}