Bug 222: Added basic Restconf operational statistics

Added basic restconf statistics which counts
incoming requests and exported it via Config subsystem.

Export via config subsystem provides this
statistics via JMX and Netconf. In distribution, where
sal-netconf-connector is present and 99-sal-netconf-connector.xml is enabled,
Restconf statistics are also available via

restconf/operational/opendaylight-inventory:nodes/node/controller-config/yang-ext:mount/config:modules/module/rest-connector-default-impl

Change-Id: Ibd0fb6875104d1a90eeaf62271c9a2f87d2f85f0
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>
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>
Merge changes I9aa41251,Ibd0fb687

* changes:
  Bug 1703: Fixed memory leak in TransactionChain
  Bug 222: Added basic Restconf operational statistics