Fixes issue with stats on start event

[cpuguy83]

In situations where a client is called like docker stats with no
arguments or flags, if a container which was already created but not
started yet is then subsequently started it will not be added to the
stats list as expected.

Also splits some of the stats helpers to a separate file from the stats
CLI which is already quite long.

[calavera]

LGTM. I really like the new event handlers.

[icecrime]

Well, that's new (win2lin):

21:03:21 FAIL: docker_cli_events_test.go:544: DockerSuite.TestEventsFilterType
21:03:21 
21:03:21 docker_cli_events_test.go:585:
21:03:21     // Events generated by the container that builds the image
21:03:21     c.Assert(events, checker.HasLen, 3, check.Commentf("Events == %s", events))
21:03:21 ... obtained []string = []string{"2016-02-29T21:03:18.174819695Z container create 6607da1f2b310022f9aa9465b7e214686087d53f1988e2614fbbbadcf8fbe62d (image=sha256:d9551b4026f0e2950ddb557cc640871710bf88476ca938b71499305647231b82, io.docker.testing=image, name=high_easley)", "2016-02-29T21:03:18.272585767Z container commit 6607da1f2b310022f9aa9465b7e214686087d53f1988e2614fbbbadcf8fbe62d (comment=, image=sha256:d9551b4026f0e2950ddb557cc640871710bf88476ca938b71499305647231b82, io.docker.testing=image, name=high_easley)", "2016-02-29T21:03:18.299829424Z container destroy 6607da1f2b310022f9aa9465b7e214686087d53f1988e2614fbbbadcf8fbe62d (image=sha256:d9551b4026f0e2950ddb557cc640871710bf88476ca938b71499305647231b82, io.docker.testing=image, name=high_easley)", "\r", "This application has requested the Runtime to terminate it in an unusual way.", "Please contact the application's support team for more information.\r", "runtime: failed to create new OS thread (13)"}
21:03:21 ... n int = 3
21:03:21 ... Events == [2016-02-29T21:03:18.174819695Z container create 6607da1f2b310022f9aa9465b7e214686087d53f1988e2614fbbbadcf8fbe62d (image=sha256:d9551b4026f0e2950ddb557cc640871710bf88476ca938b71499305647231b82, io.docker.testing=image, name=high_easley) 2016-02-29T21:03:18.272585767Z container commit 6607da1f2b310022f9aa9465b7e214686087d53f1988e2614fbbbadcf8fbe62d (comment=, image=sha256:d9551b4026f0e2950ddb557cc640871710bf88476ca938b71499305647231b82, io.docker.testing=image, name=high_easley) 2016-02-29T21:03:18.299829424Z container destroy 6607da1f2b310022f9aa9465b7e214686087d53f1988e2614fbbbadcf8fbe62d (image=sha256:d9551b4026f0e2950ddb557cc640871710bf88476ca938b71499305647231b82, io.docker.testing=image, name=high_easley) 
 This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information.
 runtime: failed to create new OS thread (13)]

[cpuguy83]

lol, StatsAll has passed twice.

[cpuguy83]

One little change to remove the not-neccessary "close" function on the event handler.

[tiborvass]

LGTM