Convert source module format from ES6 to CommonJS

The es6 module transpiler currently doesn't have a way to exclude 3rd
party libs which meant we have had to keep copies of React lib files
converted to use es6 module imports in our repo, this is bad practice as
it means we are unnecessarily locking react bootstrap to a specific
react version. This change swaps the module format to CommonJS which
(for the moment) has more mature tooling support allowing this
functionality.