Replace Negotiation Manager with Proposal Manager

[lucekdudek]

What have been done

• Replaced Negotiation Manager with Proposal Manager
• Plugins from Demand and Agreement Manager were moved to Proposal Manager
• Introduced scorers and negotiators plugin like object used by Scoring and Negotiating plugins in Proposal Manager (old plugins from Demand,Negotiation and Agreement Managers)

  demand_manager = RefreshingDemandManager(golem, payment_manager.get_allocation, payload)
  proposal_manager = DefaultProposalManager(
  golem,
  demand_manager.get_initial_proposal,
  plugins=[
      Buffer(...),
      NegotiatingPlugin(
          proposal_negotiators=[
              AddChosenPaymentPlatform(),
              RejectIfCostsExceeds(1, LinearAverageCostPricing(...)),
          ]
      ),
      ScoringBuffer(...,
          proposal_scorers=[
              MapScore(LinearAverageCostPricing(...), normalize=True, normalize_flip=True),
          ],
      ),
  ],
  )
  agreement_manager = DefaultAgreementManager(golem, proposal_manager.get_draft_proposal)