Resolve "Selector for schedule editing #861m3zvu4"

Closes #278 (closed)

Please Note: I added a dummy variant of the RccDaysInWeekSelectorComponent to the default theme to avoid 'not a known element' errors during development time and have type hinting when working on templates. We should remove that when it becomes clear that RccDaysInWeekSelectorComponent will only be used by components within Bengal themes module, or replace it with a working variant at a later time. The way theming is set up we will either have to deal with dev time errors or implement stubs like these. I'd rather do the latter, but if that is against the way things are supposed to be done please let me know and I'll remove it.

I have also implemented a little directive called RccColorCategoryDirective to solve the 'a color for selected days can be passed' criterium in a way that might be generaly usefull in the future. With this you can add css color variables to any host, so components don't have to each implement their own coloring solutions. Please see it's documentation for usage info and examples.