Issue 20 - part 1: hash cache modification

1. Modify HashCacheClient:
    a) Add List<Expression> for ON expressions of the hashed table.
    b) Change static incremental JOIN_KEY_ID to UUID.

2. Modify AgeOutHashCache:
    a) Change hashCache key type from ImmutableBytesWritable to ImmutableBytesPtr, value type from Result to Tuple.
    b) Evaluate hashmap key against ON expressions serialized by the client.