Fixed IRailAPILiveboardCommand

Changed instance method for class method
Removed `assign` property attributes

- Replaced `assign` property attributes by `weak` where needed
- Removed `assign` altogether where appropriate

Other cosmetic changes:
- Replaced some `- (id)init` to `- (instancetype)init`
- Replaced some `_object` by `self.object`
Implemented some missing objects

Added:
- `- generateStationForNode:` now parses the `sid`
- `IRailVehicle` now contains the vehicle location
- `IRailArrivalDeparture` now contains `direction`
Code style refinements

Better use of space and { placement
Merge pull request #2 from jncn/master

Added missing objects and refinements