Transaction support

[hayhay27]

Could we find a way to adapt interface to support transacitons on scheduling?

Needs to support mongo transactions alongside with psql (upcoming impl) ones.

I see that there is interface IAdderJob which has two methods AddJob and AddRecurrentJob. But they can't be extended correctly for all implementation without additional abstraction (let's say context)

Also probably we need to extend Schedule method to accept transaction (context).