Translate global jobs listref into list variable.

(This will reduce the number of patch chunks in the next commit.)
Refactored database subroutines into a separate module, CleanDB.pm.

I added 175 lines in a module in order to delete 40 lines of code from the
 main script!  But this should be easier to maintain and make it possible
 to share a single code library with the planned web interface.
Allow job deletion, and ignore single characters in command history.

1. Added an option to the job edit workflow to allow job deletion.

2. Removed single characters (e.g. Y/N confirmation prompts) from the history
of recent commands (which depends on autohistory, not maintained manually).
Added a new command 'r' to manage region names (add/delete/rename).

You can now, if you want, delete all the regions and leave that field
unassigned when creating jobs, although the script will always ask you
to define a new region instead.  You can also add and rename regions
outside of the normal add/edit job workflow.

This commit also updates the README to summarize the changes since the
last push to Github.