BVR ref is set in GP even for LSV,DD contract groups.

- [NEW] BVR ref is always set in GP
- [FIX] CODESPE can be empty in draft state, must be set before validating
  	a contract.
- PEP8 corrections
New wizard for cancelling contracts.

Instead of directly cancelling contracts, a wizard asks for ending reason
and will update child status and everything (must still be implemented).