Add XOR filter as a selectable option

The module itself is great - add's an OR extension to default AND contextual filers. I guess the title says it clearly that this is OR filer. Nevertheless working on a customer project I came up to the need on having a XOR filer.
Further digging into the problem I discovered that module is tightly coupled to a single statement choice of OR or AND, which is not quite flexible.
So to meet the needs for the client project requirements I have created this patch to extent the module with type dropdown selection - AND,OR,XOR.
Opening this solution for public testing and further discussion