EZP-21118: Implement HTTP CORS support

http://jira.ez.no/browse/EZP-21118.

Implements a Cors Configuration Provider for REST. Based on a modified version of nelmio/NelmioCorsBundle.

Looks up the OPTIONS route that matches the URI, and uses the `allowedMethods` attribute (created by the REST `OptionsRouteLoader`.

# Dependencies
- ezsystems/ezpublish-community#89
- nelmio/NelmioCorsBundle#16

# TODO
- [x] Push bdunogier/NelmioCorsBundle#1 to the real repository, then update dependencies (requires release of bundle)
- [x] Create separate issue for the `DefaultRouter/ConfigProvider` bugfix, and edit message