Uscan: add templates for CRAN and Bioconductor

This MR adds uscan templates for two archives of R libraries:

• CRAN (https://cran.r-project.org/web/packages/index.html)
• Bioconductor (<https://bioconductor.org/packages/)

We use them as the source for the r-cran-* and r-bioc-* packages in Debian.

Repacking is frequent because the upstream sources often ship HTML documentation containing minified Javascript. Hence the proposed templates declare a standard repack suffix and provide mangle rules to handle it.

After this MR is accepted, when can we start using the templates in watch files?