New API for WebSocket support

- API
 - @websocket decorator
 - WSGIApplication#websocketmanager()
- bugfix
 - Even if a connection is cut, it continues remaining
- remove restriction
 - Two or more connections can be accepted

Signed-off-by: Satoshi Kobayashi <satoshi-k@stratosphere.co.jp>
Reviewed-by: YAMADA Hideki <yamada.hideki@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
sw test tool: Remove an unnecessary wrapper method

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Reduce similar methods of event handlers

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Reduce similar classes

TargetSw and TesterSw are merged as OpenFlowSw.

And to avoid pylint error, add dummy methods to DummyDatapath.

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Reduce similar methods of deleting flows

And rename del_test_meter() to del_meters(), like del_flows().

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
sw test tool: Reduce similar methods of initializing flows

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>