port features from simple cms into routing bundle to simplify things

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes (small ones)
| Deprecations? | yes
| Tests pass?   | not yet
| Fixed tickets | #156, #149, https://github.com/symfony-cmf/symfony-cmf/issues/182
| License       | MIT
| Doc PR        | https://github.com/symfony-cmf/symfony-cmf-docs/pull/430

This attempts to port some features from SimpleCmsBundle to the core route, to simplify things and because they make sense outside of the simplecms context too.

The most important change is that the RouteProvider and the PHCPR-ODM listeners now support more than one prefix. This should hopefully get us rid of the whole duplicated router business with all the problems it brought.

I also propose to add an option to optionally have the locale listener automatically set the addLocalePattern on routes that have no locale from their id - it is a rather extreme case that you would need to set that individually per route.

* [x] Update configuration for multiple base paths
* [x] Check the locales support
* [x] Get tests to succeed again
* [x] Check for leftovers in the PR
* [x] Adjust admin class
* [x] Add BC code for the move to $options and document migration in UPGRADE.md (should we keep even a BC mapping, or only the methods?)
* [x] Refactor ORM to also use candidates

/cc @benglass i would love to hear your feedback on this.