The widgets should be really moved to a separate js project (still inside coreapps) so they can be developed and tested with js tooling (webpack, babel, jasmine, etc.). It will be similar to how we develop OWAs in modules, see e.g. https://github.com/openmrs/openmrs-module-openconceptlab/tree/master/owa
I may be able to change that by the end of this week. To be honest I wasn’t expecting others to pick up our work on widgets that soon 
It’s great to see that though!