Explain how to extend theming and styles

[siddharthlatest]

React components have a bad history[1][2] of being extensible with user specific style pre-processors. We should highlight this aspect clearly in the project, in fact, it can be a page by itself in the main docs.

Key points to highlight:

1. Show a live example of an interface styled with both Bootstrap and Material, and then explain how to switch between the two and / or use any other UI styles framework.
2. Document the class name hierarchy and naming convention used within the components so they can be extended by a user easily.
3. Show how to extend the library sass variables to affect UI theming.

[1] https://news.ycombinator.com/item?id=13053547
[2] https://news.ycombinator.com/item?id=12939651

[siddharthlatest]

Styleguide explained here - https://opensource.appbase.io/reactivemaps/manual/v1/getting-started/StyleGuide.html as well as in each individual document.

Using built-in theming explained here - https://opensource.appbase.io/reactivemaps/manual/v1/getting-started/Theming.html.

Extending the library sass variables will be explained in advanced section of the manual.