Task Executor - Milestone 3 (Code Complete)

This commit marks the Task Executor as functionally Code Complete. It has all described functionality except outputGroups (since that requires major plumbing in other parts of the code). 

- [x] Multi JVM Executions (multiple capability spawners)
- [x] Overall User Input prompts (outmost task)
- [x] Just-in-time user input handled (later inputs for capabilities/subtasks)
- [x] Can handle multiple end points (multiple exits)
- [x] Can handle various execution times of capabilities
- [x] Exits cleanly (using kill messages, kills spawner(s) too)
- [x] Async Message handling
- [x] Manage diverse capability DAG structures (no assumptions)
- [x] Plumbing with Resolver, appropriate callback-type mechanism for web conversion (out of scope)
- [x] Full Dag Test case (NewCombo.xml)
- [ ] Demonstrable
- [ ] Meaningful Test Case
- [ ] OutputGroup Functionality
- [ ] Custom User Prompt for the just-in-time inputs