modify config.json , add the config parameter for database connection.
Add a REST API (method=POST) for statistic in core.py
1. add the statictis handler for statistic query
2. connect to mongodb
3. result is tsv format
1.UIPusher will store the diff of flow-counter every 5 second
2.store the flow-counter to db
1. use a function to handle the db
2. if this time's diff-cache will cross the time-zone, store the diff to
db immediately
Set the fetch interval to 30 seconds.
Merge pull request #23 from hwchiu/stat-core

Stat core