New feature: flexible backup periods

[Brian Smith <brian linuxfood net>]

Hi!

Over the weekend I came across deja-dup and found that I really wanted
to do backups every 3 hours. So, I built the feature. It was a
relatively easy change (aside from learning gtk and vala), so I didn't
reach out beforehand.

The branch is https://code.launchpad.net/~linuxfood/deja-dup/flexible-periods

I'm hoping that I can work with everyone to improve the code to the
point that it can be merged.

Thanks in advance!

-B