datetime picker step property is not set on the backend

If you add a <vaadin-date-time-picker step="1"></vaadin-date-time-picker> component to a page, it will ignore the initial step property value. (And all other property too)

This is related to #356 (closed) because the interceptor doesn't set the property on the backend component.

This can be easily fixed by checking which property is overriden by the backend component, and setting them in the interceptor, but, maybe there's a better option for this that worth investigating:

• Either figuring out how the frontend initial states could be synched to the backend (this would be useful for other components as well)
• Or by solving the i18n problem in another way (interceptors are not our friends anyway 🙂 )

(high priority, because with the current solution, this can only be resolved in user code, by implementing a different interceptor, and hoping that will be the first on the classpath 🙁 )