sc 0.50.0, codec 0.19.0, vm 0.8.4, sdk 0.4.1

• Framework now runs on stable Rust. All unstable features were removed. The most important changes enabling this:
  • CodecFrom completely removed, TypeAbiFrom was used instead since 0.49.0.
  • ManagedVecItem payload redesigned.
  • Contract panic message mechanism improved.
• Unified syntax:
  • NotPayable marker type in proxies, which prevents callers to add payment to a non-payable endpoint.