rename "Model" to "DAG"
remove pass-through from non-parallel tests
rename some tests
remove duplicate of "single_operation" test
move code from CommandOperation to command mixin
make parallel mixin not inherit from pass through
add color to job unique constraint
remove backref from Method to Command
add parallel by command functionality
stop using pass-through in tests
remove implementation references to pass-through
extract base petri mixin
add converge operation
auto-detect operation type
make tests rely on op-type auto detection
Revert "add converge operation"

This reverts commit e3603a9e1c22efc1d222591bc3d1f4e75af62b3e.
Merge pull request #9 from mark-burnett/cleanup-op-types

Cleanup op types