Map based Adsdimension demo

A Map based implementation Adsdimensions Demo, following parts are implemented
- A generic mechanism to specify schema for input. We still need to come up with a way to send the schema to
  DimensionComputation and HDSOutOperator. Sasha is working on that.
- A Map based aggregator to be used with DimensionComputation.
- A Serializer which serializes keys and values to be used with HDS, and reconstruct these from byte array.
- A QueryOperator to retrives data from cache as well HDS for give key.
- A sample Demo Application.

Sample Demo application is in working state.
aggrDesc -> aggregations

Entire fields declaration can go away. All we need is keys and aggregations. For example we can specify  clicks as "clicks, sum, int" in one place.