Wrap backend output in various classes and add #akeeba-strapper.

Also refactored preRender(): return immediately when $platform->isCli()

Github had issues with the diff and PR so I created a new one. This is updated version of:
https://github.com/akeeba/fof/pull/339

> I'm thinking that this is security nightmare as it puts in indexable HTML the component name, view, layout, Joomla! version etc. Maybe drop our pants, lubricate our anus and bend over too? I'd say that we need to replace if (!$platform->isCli()) with if (!$platform->isAdmin()) and add an elseif (!$platform->isCli() block which outputs only the Akeeba Strapper ID and the Joomla! version class, with the prospect of removing the J! version classes from it in FOF 3.

Mzz you've got a good point regarding security... I've altered it and only output the new classes in the backend. I think this is ok?