Adjusting template to use new DOI/URL/URN naming scheme of tuprints.

Hi folks, As discussed in #520, tuprints has introduced a new naming scheme as follows (including the order): * DOI: https://doi.org/10.26083/tuda-1234 * URL: https://tuprints.ulb.tu-darmstadt.de/handle/tuda/56789 * URN: https://nbn-resolving.de/urn:nbn:de:tuda-tuda-567890 Since I am about to publish my dissertation, I needed a *quick fix* that works for now. I am sharing this here for other "fellow sufferers" who may be affected. It may not be complete or technically versatile, so feel free to adapt it. I use LaTeX directly on my local machine, not ShareLaTeX/Overleaf, just FYI. @TeXhackse: Thanks for the awesome template. 😃 This PR fixes #520.