Return all services for given transport mode from service store

[geertw]

The service store should be extended to return all services using a given transport mode for a given service date. This allows for example to select all rail replacement bus services from the service store and inject them to the InfoPlus DVS application.

To implement this feature, the following should be done:

• Store in Redis a set of all services for a given service date per transport mode
• Add a method to the service_store module to retrieve all services for a given transport mode (for a service date)
• store_service() and delete_service() should add/remove services from the transport mode set in Redis
• Unit tests

[geertw]

Functionality removed because it wasn't used in the end (a more efficient algorithm for filtering services was implemented) and because it caused a lot of headaches for removing services.