🧹🚀 Housekeeping before v1.7.0 release

[cthoyt]

This PR has housekeeping before the 1.7.0 release. It does the following

1. Writes the 1.7.0 changelog (wow, we did a lot!)
2. Renames StructuredEmbedding to SE and UnstructuredModel to UM. This is a breaking change, but does anyone think it will have a big impact?
3. Update the README to include not only the models, but also the interactions in the same table. This was motivated by the fact that we've got a few interactions that don't have associated models that I still want to count towards our grand total (e.g., TransformerInteraction)
4. Make all interactions importable from the pykeen.nn interface. In fact, a lot of our modules should actually be available through this, like pykeen.losses, but this is a problem for a 2.0 release.
5. README updates
   • add full DOI for published benchmarking paper 🚀
   • Add additional DARPA funding (does anyone have any updated stuff they want to add?)

Let's plan to send this on Tuesday. Please send any comments by then.

[cthoyt]

@PyKEEN-bot test

[cthoyt]

@PyKEEN-bot test