Solve problems with job statuses in GH facade

[nieznanysprawiciel]

• Status reverts from Finished to Idle #141
• Job is not displayed when Activity was destroyed, but Agreement not terminated #147
• Empty activity list from monitor sets CurrentJob to null #148
• Job status remains Computing after kill #150
• Job status after app termination before payment ya-runtime-ai#80
• CurrentJob set to None in between activities #118

Problems to be solved as separately

• Race conditions between Interrupted job and Requestor attempting to terminate #164

Testing scenarios:
https://github.com/golemfactory/gamerhash-facade/wiki/Task-statuses-%E2%80%90-testing-scenarios
List of scenarios is not closed yet.