Client: use defined status in crab utility.

The crab utility now reads the status codes from
the CrabStatus class rather than constructing them itself.
Client: add --stdout and --stderr file options.

Now when reporting a job finish event using the crab
utility, the standard output and/or standard error
can be provided as files, or read from standard input.
All: add generic WARNING finish status.

This is a warning-level status which can be used when
none of the other status codes are appropriate.
Client: silence stdout/stderr file read errors.

Instead of printing an error on failure to read these
files, the crab utility sets the finish status to warning
(provided it was OK to begin with).  This should prevent
unwanted emails from cron if this facility is used in a
cron job.
Web: add job delete/undelete controls.

This required adding public delete/undelete methods
to CrabStore.

Previously the only way provided to delete jobs was to import
a new crontab from the host in question, but that might
not be easy if the host is down or otherwise inaccessible.