Implement OR for events filter pushdown

[hakontro]

The current implementation of Events filter pushdown will find all types/subtypes that are present in a query and provide the cartesian product.
Hence filters like (type = a and subtype = b) OR (type = c and stubtype = d) will read (a,b)+(a,d)+(c,b)+(c,d) rather than just (a,b)+(c,d).

[hakontro]

This is handled by Spark in a later stage, so it works.