Update SQMtools (and R recommendation) to >4.0

[fpusan]

This would involve

• Checking that SQMtools works in R>4.0.0
• Checking that DAStool R package works with R>4.0.0
• Updating / testing the conda recipe to include R>4.0.0
• Updating / testing the Ubuntu/CentOS instructions to use R>4.0.0

[fpusan]

Everything runs fine with R>4.0.0, but eventually the conda installation started failing because of some bioconda.bioconductor package. I opened the R4 branch with the necessary changes to the conda recipe, hopefully at some point the conda package will become stable enough.

[fpusan]

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