Run actions w/o scheduler

It turns out that using scheduler to run actions doesn't make a lot of sense for the reasons below:
1) Reliability (sync between DB and MQ) is still not guaranteed, the problem (concurrency windows) just moves into Scheduler where it's supposed to be solved but, in fact, it's not solved
2) Significant loss of performance: a) Scheduler iterations run with a delay (1 sec) 2) Unnecessary DB queries

For those reasons we should move away from using Scheduler to run actions. The problem of reliable scheduling should be solved in a different way when we approach failover functionality (essentially, we should allow to fix 'hung' workflows manually by either failing them or providing result directly).