Part of #2040 and takes care of part of Router
Related to #2049

Convert from FlowRouter to React Router.

Things it must do:

• Must not be a breaking change for those that used the registry to populate their custom routes.
• Must render a react layout, which means the main app layout needs to be wrapped inside a react component at least.

This will be a breaking change for those that may have defined routes by means other than the Reaction Registry.