Bug 1703: Fixed memory leak in TransactionChain

Bug 1703: Fixed memory leak in TransactionChain

As it turned out WeakHashMap is not cleared
if value has strong reference to key. This
required to rewrite BindingTransactionChain
to listen on submit futures for each  transaction
in order to receive events mapped to binding transaction.

This actually simplifies code and removes
any need for having canonical mapping from
DOM transaction to Binding transaction.

Change-Id: I9aa4125197b022dd163f85c6965ad1227e771b99
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>