Clean up attributes in fed-gen

[cmnrd]

#1221 introduces several new attributes. Some of them are overly general (@languange) and others are redundant. This PR cleans up the newly introduced attributes.

This PR also includes some additional small cleanups including resetting .idea/codeStyles/Project.xml to the version from master.

[lhstrh]

I think the changes you made here make sense. That said, I think that it might be cleaner to just reserve a single @generated attribute for code-gen-related stuff and just have key-value pairs in it. I think that's neater than a _ prefix, which looks ugly (let's not use underscores in these at all). We can change this later because this only concerns cosmetics and isn't user-facing.