Fork/retire "ccdR" with warning for "ctxR"

[madison-feshuk]

• Fork "ccdR" repo
• Rename forked repo as "ctxR" for "CompTox and Exposure" instead of CCD. Python client will use similar name, ctxPy
• Add warning message after attaching library --> "ccdR is no longer maintained and users should check out ctxR instead."
• Push final ccdR update to CRAN