Added slow start to ConsumerWindow

Added slow start mechanism to ConsumerWindow. Removed m_maxSize and m_payloadSize since they just confuse the users and don't really do anything more than m_seqMax.

Another point to note is that timeout events should be intepreted differently when hop-by-hop interest shaping and NACK are enabled. When those mechanisms are in place, congestion is signaled by NACK and timeout should happen very rarely (only if we encounter imperfect interest shaping or NACK loss).