add ET paper examples to gallery

[Roland Haas]

The examples given in the ET papers: http://arxiv.org/abs/1111.3344 and http://arxiv.org/abs/1304.5544 should be added to the gallery. For the original ET paper the parfiles are already being shipped with the ET: https://bitbucket.org/einsteintoolkit/einsteinexamples/src/master/par/arXiv-1111.3344/ while the MHD paper has them on: http://einsteintoolkit.org/mp.html

This would also ensure they actually work and avoid issues such as #2373 and (much longer standing) http://lists.einsteintoolkit.org/pipermail/users/2019-March/006803.html and similar ones as well as eg missing date files for the stellar collapse example .