#9 Implement dictionary fast sorting

[Bors]

Need to implement fast sorting for the following cases:
1. Sorting cardinality is low comparing to the number
of entries to sort. Need to implement fast bitmap
sorting.
2. Sorting cardinality is high but number of groups is
huge comparing to the number of entires within the
group. In this case need to pack entries as dictionary
and pass it to the coordinator as numbers rather than
entries.