make rest controller more generic to support additional workflows

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | #116
| License       | MIT
| Doc PR        | TODO

/cc @uwej711 

btw for the doc, this is using symfony http handling, meanign X-HTTP-Method-Override is supported as well.
well, for `DELETE` there is a configuration option to even enable it: https://github.com/symfony-cmf/symfony-cmf-docs/pull/540

when starting to use workflows for other things, you should register an [AccessChecker](https://github.com/symfony-cmf/CreateBundle/blob/master/Security/AccessCheckerInterface.php) - this has the additional advantage that you can allow different things to different users.