Set up new isoband website or remove links

[clauswilke]

There used to be an isoband website at https://wilkelab.org/isoband/ but this now no longer works since the repo now lives in r-lib. Following the convention of other packages in r-lib, the site should probably live at https://isoband.r-lib.org/, but that doesn't seem to be automatic.

Also, there are various references to https://wilkelab.org/isoband/ throughout the package and the github repo that need to be fixed or deleted.