Add minimal genomes possibilities

[maxulysse]

• Add no_intervals params
• Add automatic generation of intervals file with BuildIntervals process
• Add minimal support for minimal genome (only fasta, or fasta + knownIndels)
• Add new processes (IndexBamFile, IndexBamRecal) to deal with optional usage of interval files and minimal genome
• Add tests for minimal genome usage
• Add new minimal genomes (AGPv3, BDGP6, CHIMP2.1.4, CanFam3.1, EB1, EB2, EF2, EquCab2, GRCz10, Galgal4, Gm01, IRGSP-1.0, Mmul_1, R64-1-1, Rnor_6.0, Sbi1, Sscrofa10.2, TAIR10, UMD3.1, WBcel235, bosTau8, canFam3, ce10, danRer10, dm6, equCab2, galGal4, hg19, hg38, mm10, panTro4, rn6, sacCer3, susScr3) to igenomes.config
• Some process (BaseRecalibrator, ApplyBQSR, Mpileup) have now optional usage of interval files
• Update comments

PR checklist

• This comment contains a description of changes (with reason)
• If you've fixed a bug or added code that should be tested, add tests!
• If necessary, also make a PR on the nf-core/sarek branch on the nf-core/test-datasets repo
• Ensure the test suite passes (nextflow run . -profile test,docker).
• Make sure your code lints (nf-core lint .).
• Documentation in docs is updated
• CHANGELOG.md is updated
• README.md is updated

Learn more about contributing: guidelines

[apeltzer]

Amazing stuff @maxulysse !

[maxulysse]

Needs docs