[Users] Einstein Toolkit bibtex file clean-up

I just cleaned up the Einstein Toolkit bibtex file. The most prominent changes were (a) using consisten entry names if the entry is not in Spires; I followed the existing convention of inventing a Spires-like name in this case instead of choosing different format for the entry name. I also (b) ensured that the eprint entries show up correctly; Spires splits up eprint entries into eprint, archivePrefix, and primaryClass, which are unfortunately ignored by most bibtex styles.

I realise in hindsight that this is a substantial change; if you disagree, I will revert this change, and we can then discuss it.

-erik