Finagle example.
Extract common code for Main classes from examples.

This changes how the mains are run. Previously one could run
  - `java -jar server.jar -init`
  - `java -jar server.jar -serve`
  - `java -jar server.jar -init -serve`

Now one can run:
  - `java -jar server.jar init`
  - `java -jar server.jar serve`

Previously the `-init` and `-serve` were flags that could appear anywhere in the other flags. Now `init` and `serve` are commands that must appear first. Previously, one could init and serve in one run. Now they must be separate runs.

closes #51
Include cell ID when logging "accepting connections."

Reporting the host and cell makes easier to start another host, hail and join the cell, or simply migrate the disk.

closes #50