Fix filtered agg 0.7

1) fix NPE when value or dimension is not presnet
2) fix #872 
3) Add more tests for boundary cases
4) Add support for AND & OR filter, allowing filtering on multiple dimensions 
5) code cleanup
6) behavior of empty columns - they are treated equivalent to all rows having null/empty values
I think this changes behavior. Before an empty and filter would always return true, now it returns false.