Implement Advanced Execution Flow Control

[dafreels]

Provide additional behaviors to an execution:

Conditional:
The execution should have the optional ability to execute one or more pipelines to determine how an execution should be executed. Three valid statues should be returned from an evaluation:

• RUN (default behavior)
• STOP (error behavior)
• SKIP (new behavior)

Fork:
An execution should be able to fork into multiple process (like the fork pipeline step) and execute in parallel.