Merge ParallelByTask and Task

This introduces a few if statements but allows us to eventually
eliminate the Node abstraction with Task.
Move logic to node_base

Most of the petri-construction logic.
All of the input/output logic, including parallel-by related logic.
Eliminate _method_place_name from Task
Rename Task to MethodList
Rename node to task (in the code)
Rename node to task (in the dsl)
Merge pull request #27 from davidlmorton/merge-task

Merge Task and replace Node