Change duration in millis to Duration everywhere.

- Redo AbstractFSCommitter to favor composition.  In fact, see if we 
  can redo most to avoid that much inheritance.

- Create README.txt in delete directory to explain
  how files can be copied back if wanting to resume them.

- Do a memory committer queue and test swapping one for the other behaving
  just fine.

- Ensure no workDir collision (either in this project or caller).  Append
  committer index in case of multiple committers (or always)?

- Have installer for other committer?

- Committer server (and a committer "client" that can round-robin between 
  committer servers?)
 
- Add chainable committers??
