Move logic back to ExecuteCases from ExecutionModel allowing ExecutionModel to focus more on the graph of behaviors rather than the inner workings of those behaviors.
Fix name of RunnerTests.
Move RunnerTests to appropriate namespace.
Move RunConvention(...) from Runner to ExecutionModel, because that's where all of the routine's state lives.
Extract Method for the handling of the 3 kinds of tests results (skip/pass/fail) in the main convention-running loop.
Extract behavior chain ownernship from ExecutionModel by adding ExecutionPlan.
Move ExecutionPlan to its own file.
Rename ExecutionModel to ConventionRunner.
Drop ExecuteCasesTests as redundant and too fine-grained.