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#
- bdunogier/NelmioCorsBundle#1

# TODO
- [ ] Push bdunogier/NelmioCorsBundle#1 to the real repository, then update dependencies (requires release of bundle)