Speedup filter groups

[GregorCH]

speed up IPET evaluation considerably through

• grouping all active filters and reusing already computed results from equal filters across filter groups
• reusing the same set of intersection rows across all filter groups
• replacing some apply operations by bitwise ands

[GregorCH]

Thanks for your review, I modified the corresponding places in the code, and added more documentation and meaningful assertion messages to the new test.

[fschloesser]

Alright, this is ready to merge then.