Make the max list depth configurable

[brieb]

First off, thank you for the awesome plugin! :)

In our app we want to support 7-depth lists and this plugin was forcing the limit to 4. So, we wanted to add a configuration option for setting the max list depth.

[brieb]

Note that if more levels of nesting are needed, the necessary CSS classes need to be provided via blockStyleFn configuration.

https://github.com/facebook/draft-js/blob/3da87b518fa090da1c30b866914fe06586bb97a2/src/component/contents/DraftEditorContents.react.js#L264-L290

facebookarchive/draft-js#997

[thibaudcolas]

Just an FYI that I had a similar use case for configurable max list depth in my own editor, so I made a little helper component that automatically generates the necessary CSS: https://github.com/thibaudcolas/draftjs-conductor.

With this added, you can configure the max depth per-editor without having to make styles "just in case" even when unnecessary. Using the helper looks like this:

import { ListNestingStyles, blockDepthStyleFn } from 'draftjs-conductor';

<Editor blockStyleFn={blockDepthStyleFn} />
<ListNestingStyles max={7} />