Extract app and keys (#276)

* Extract app component from entrypoint (index)

- Use refs to refer to canvas and rough context
- Remove ReactDOM double rendering

* Extract keys and key related utils into their own module

* Move everything back to entrypoint

src/element/textWysiwyg.tsx

@@ -1,4 +1,4 @@
-import { KEYS } from "../index";
+import { KEYS } from "../keys";
 
 type TextWysiwygParams = {
   initText: string;