Refactor SU creation elements

• extract common functionality in SU creation for single + multiple and implement them in create+excelview plus tests

     - Project + Scheduling Set Selector
     - ObservationStrategy selector with purpose and state filtering 

What that means in the front-end:

• rewrite Numeric Editor to adhere to new coding standards (not React15) + unit test
• extract leaf function from excel view to helper + test
• set basic tests for excel view editor so it tests at least something + TODO
• make test helpers better
• test + refactor two methods in the validator to not use 'replaceAll' as it is not accepted in the pipeline