add websocket support to /container/<name>/attach/ws

This function add the possibility to attach containers streams to a
websocket. When a websocket is asked the request is upgraded to this
protocol..
put the websocket route in the map containing all routes

Instead of handling the websocket differently just handle it as a normal
route and upgrade it to a websocket.
useless type
useless function. forgot to remove it.
reuse the type
Merge branch 'feature/attach_ws' into feature/attach_ws2

Conflicts:
	api.go
Merge pull request #1146 from benoitc/feature/attach_ws

* Runtime: add websocket support to /container/<name>/attach/ws