Feature request usability: filter by multiselection

[ChristianMayer]

When I select a tag in the list on the bottom right this tag is immediately used as a filter on the image list on the left side. This is great.
But when I select multiple entries only the last one is used for the list on the left.

My expectation was that this multiselection is creating a filter where the entries are either ANDed or ORed together. I.e. the union or the intersection of the selection is shown. Both are valid expectations.

So my feature request is:

1. The multiple tags are selected all of them should be used in the filter (it's your decision whether that means AND or OR)
2. Enhancement to 1.: depending on the press of a modifier key like "alt" an additionally selected tag is added to the filter in the opposite fashion. (E.g. normally all tags are ANDed, then a alt+click would add that tag with an OR)

[maedtb]

I've wanted this behavior as well, but when I looked into it, it appeared as though it was previously supported and then quickly removed (Removed CL: d22442b)

@jhc13 Is this an undesirable feature, or were you just unhappy with the implementation?

I propose it be readded, but via two new Click Actions: Filter Images for All Selections and Filter Images for Any Selections. This maintains the current behavior, but gives users the ability to perform advanced actions.

I also want to propose a No Action click action, which causes selecting tags to not affect the image list or image tag list. This is useful when performing tag renaming and when a use would generally like to browse the global tag list without affecting the current image or filter. I've added this to my local TagGUI form and I have found it to be useful.

If this is acceptable, I'm happy to implement it and send a PR.