Add additional condition for executing steps

Add conditions for executing steps that would need multiple steps to succeed (conditions from multiple parents for execution) or steps that could depend on a step from a different stage as well as their parent.

For example:

stage A:
  step1
Stage B:
  step1
  step2 - execute step2 if step1's RESULT is OK and if <string> is in (stage A - step1)'s $output