Display version of resource in public-facing HEASARC tutorials website

[DavidT3]

Add the version number under the HEASARC logo and automatically update it with new releases.

[DavidT3]

What might be potentially nice is to have a version switcher GUI element, like you get on readthedocs - that would be one possible way to have a dev version as well (see issue #171), if that is something I end up wanting to do.