[#425] services: Define service interfaces that was removed from API lib

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/session/executor.go

@@ -16,7 +16,7 @@ type executorSvc struct {
 }
 
 // NewExecutionService wraps ServiceExecutor and returns Session Service interface.
-func NewExecutionService(exec ServiceExecutor) session.Service {
+func NewExecutionService(exec ServiceExecutor) Server {
 	return &executorSvc{
 		exec: exec,
 	}