status: New builtin for system administrators to see deployments

This allows administrators to configure between deployments and easily see which deployment
they are booted into as well as indicating which is chronologically most recent.  This makes
the process more user-friendly, rather than requiring the user to remember which deployment
checksum corresponds to the most recent upgrade.
status: Rework code organization and readability

This includes several changes to format the code to follow GNU Coding Standards as per
the restof rpm-ostree.  This includes fixing indentations, adding spaces between
identifers and parentheses, replacing "goto print" with an else structure, and
reformatting print statements into complete sentences for internationalization.
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.