More functions for splitters

[Ibonann]

We can input 4 separeted ressources to Splitters but it can only handle up to 3 without doing sushi belts. Choosing a second filter would help to sort belts from AB|CD to AD|CB.
And there is one more missing feature:
Splitters cannot split a single ressource into a belt with only left and a second with only right side output. Thats only possible with 2 different items and the filter. What we would need is a side option for the filter instead of the item. And combined with a second filter it would also work with 2 Items.
Example: Input AA|B- ; Filter B + right side ; Output BA|A-