Merge remote-tracking branches 'upstream/master' and 'origin/openflow-1.3' into openflow-1.3
1. Create new type StatsReply to encapsulate the return value of the
method retrieve on SwitchStatisticsResource.java
2. Adding a custom serializer to serilize the StatsReply.
3. It only supports statistic_flow type and OF1.3 format now.
Merge branch 'openflow-1.3', remote-tracking branch 'upstream/master' into openlow-1.3#Serializer
replace the tab with 4-space
Merge pull request #2 from hwchiu/openlow-1.3#Serializer

Openlow 1.3#serializer