Add systemd units for running Snapper scripts

Add systemd units for running Snapper scripts

Snapper uses cron jobs to schedule hourly and daily snapshot creation
and cleanup scripts. Instead of using cron, Tizen should use systemd
timer units in order to manage these jobs.

Updating: The spec file for Snapper has an obsolete file
(/etc/sysconfig/snapper) that needs to be replaced for this to work
correctly. As the file is intended to be updated manually I have
decided that users who are updating rather than reinstalling should
add the 'SNAPPER_CONFIGS="root"' line to their /etc/sysconfig/snapper
file themselves if they want to make use of this feature.

Signed-off-by: William Douglas <william.douglas@intel.com>