Remove node-sass dependency from muban webpack scripts

[jesse-mm]

Currently we have a node-sass dependency in muban-webpack scripts. node-sass is included as dependency of node-sass-json-importer.

Suggestion is to remove the node-sass-json-importer as dependency. Add the code of the library to our scripts as the dependency is unmaintained. On top of that node-sass is not required for that dependency to work.