Reintroduce `fetch()` method in ContainerController

It has been removed in commit f38fbfa373e132c0c0bd93ddcf7e658f13c6a142,
but it was still used, for instance, for the "top" action.
Fix undefined index 'stream'

AFAIU 'status' is sent instead of 'stream' for lines such
as 'Pulling repository debian'. Strategy here is to ignore
chunks that do not contain any 'stream' entry.

Fix #27
Fix undefined payload method

Twig error thrown in admin dashboard
Finding a container must be done by the container manager
Fix bad classname, FQCN is needed in constant()
Merge pull request #33 from willdurand/fix-undefined-fetch-method

Reintroduce `fetch()` method in ContainerController
Merge pull request #35 from willdurand/fix-stream-log

Fix undefined index 'stream'
Merge pull request #36 from willdurand/fix-undefined-payload-method-in-tpl

Fix undefined payload method
Merge pull request #37 from willdurand/fix-find-container

Finding a container must be done by the container manager
Merge pull request #38 from willdurand/fix-set-status-cmd

Fix bad classname, FQCN is needed in constant()