Custom Toolbar for "upload-image" doesn't appear to work

**Describe the bug**
I'm working to set a custom icon for the Upload Image button. When I do so the button no longer functions. Since the action was not documented I dug around and sussed out that it should be `EasyMDE.drawUploadedImage` and set it as such.

My custom toolbar code is as follows:

```
toolbar: [{
name: "upload-image",
action: EasyMDE.drawUploadedImage,
className: "icon-photo",
title: "Upload Image",
}],
```
**Expected behavior**
Should trigger the file chooser to find a local file to upload.

Start with the custom toolbar configuration in the issue and inspect how EasyMDE.drawUploadedImage is wired to the upload-image action. Reproduce the configuration, then verify that using a custom icon still opens the local file chooser and preserves the upload behavior.

Written by the indexing model from the issue text.