Move playground to its own repo: reactive-playground

[siddharthlatest]

We will move the storybook and associated playground build and config files to its own repo at reactive-playground. That way we can use a unified playground across all reactive* projects.

In doing so, we will also build a jquery-esque plugin to filter stories by applied tags (which can also be set as a URL query parameter)

[siddharthlatest]

We have migrated the playground for ReactiveMaps and ReactiveSearch to the https://github.com/appbaseio/playground repository. Since ReactiveBase is not public facing, we will keep the playground local for now.