Support numeric between operator

Hi @pietermouton, I have trie to implement a more generic solution in MR 30.

Could you give it a try and tell me how it goes? Thanks.

Hi @mably, I've checked the MR. Looks goods code-wise, but there's one issue (at least for me).

I have a range filter with 'within' (range contains) operator and a 'word' (contains any word) operator, but now it is added before the value as a prefix. It doesn't feel right to add the machine name of the operator over there.

For example for the 'contains any word'-operator, it seems ok to just show the value provided without a prefix. I think that's the case for most operators. There are only a few operators that might add value for the end-user.

I think only some of the numeric operators have added value to be used as a prefix: <, <=, >, >=, !=
We should add a mapper to check which operators need to be visualized.

@pietermouton do you think I can merge MR 30 or do you have other improvements in sight?