Improve atomic actions format and rename term "atomic actions" into "actions"

I. Currently atomic actions data in workload results is insufficient,
therefore some new features can not be implemented.

Wee need to change actions results schema from type "object" to "array"
and extend it with timestamps and nested actions.

II. Since we are going to support nested actions, term "atomic actions" becomes confusing because word "atomic" means something that can not include nested items. So we can get rid of name "atomic" and simply use term "actions"