Fixing DFS implementation of DAG validation to be much faster
Adding in additional tests to ensure the run order of expanded tasks is preserved
Adding additional compile-time checks, resolving issues that came up as a result
- Adding support for SlurmTaskExecutor in `daggyd` if DAGGY_ENABLE_SLURM is defined.
- Renaming some test cases
- Enabling compile-time slurm support
- Adding slurm documentation
- Roughing in FileSystemLogger
- Deleting Scheduler code and associated unit tests as being too complicated for maintenance.
- Refactoring namespaces for loggers and executors.
