yapapi Service API suspend

[shadeofblue]

• initial research (enumerate components below)

  • Golem shutdown
  • Engine shutdown
  • Cluster shutdown
  • ServiceRunner shutdown
  • instance tasks
  • agreements pool

• implement changes needed for yapapi's Service to be able to suspend without terminating activities / agreements

  • ...

• allow the state to be serialized

• entities to be serialized

  • Network - Network serializer / deserializer #1131
  • Agreement - Service API suspend / resume + a modified webapp example #1137
  • Activity - Service API suspend / resume + a modified webapp example #1137
  • DebitNote/Invoice stats