Service PID recovery

[Gandalf-]

PIDs should be saved on start up so devbot can attempt to reclaim services that survived a devbot restart.

These can be kept in the database, separate files aren't necessary. This should work on Windows too.

[Gandalf-]

This works on Windows now, but not Linux, since ^C on Linux kills the children processes.

Might be able to prevent this by masking signals to the children processes?

• http://hackage.haskell.org/package/process-1.6.5.1/docs/System-Process.html