status: Rework format into columns

After a discussion on what the status command should offer a
sysadmin, we decided to try a column output format similar to that
of systemctl or docker images.  This will print the timestamp,
a truncated checksum, the osname, and the refspec of each
deployment.  It also includes a --pretty option to print
the information formatted in rows with the full checksum and a
title to specify the default and the rollback target.