Clean up unnecessary #includes from RemoteJobManager.h

Refs #9049
More #include cleanups

Moved a few inlined functions over to the .cpp file which let me replace
two more #includes with forward declarations.

Also moved 2 member variable initializations out of the constructor's
body and into the constructor initialization list.

Refs #9049
More #include cleanups in RemoteJobManager.<h|cpp>

Replace <istream> with <iosfwd>
Remove unneeded <fstream>

Refs #9049
Merge remote branch 'origin/feature/9049_remote_job_includes'