[WIP] BDD: Update structure for the inheritance fix

This belongs to a inheritance fix that involve:
- [ ] ezsystems/BehatBundle (PR coming)
- [ ] ezsystems/ezpublish-community (PR coming)
- [ ] ezsystems/ezpublish-kernel (EzPublishLegacyBundle and EzPublishRestBundle)
- [ ] ezsystems/DemoBundle#90

Todo:
Both:
- [x] move everything into an BddTest folder (so that the Feature and Context folder be on the same level)
- [x] Update main class name to reflect bundle
- [x] Update namespaces
Only for LegacyBundle:
- [x] Move SetupWizard sub context, into a main context
Only for RestBundle:
- [x] Change Error sub context class name to Exception
- [x] Add doc into RestContext methods (for the sentences implementations)

**Needs to pass on travis**:
- [ ]  - (PR coming)