More improvments

[maxulysse]

• improve cpu usage
• use same font for nf-core and sarek in ascii art
• add --no-reports option for tests + add snpEff,VEP,merge to MULTIPLE test
• use --no-reports for TravisCI testing
• add possibility to download other genome for sareksnpeff and sarekvep containers
• update docs
• add --no-reports for all tests but MULTIPLE in Jenkins

EDIT:

• Add params --skip to skip specified QC tools
• params --noReports is now --skip all
• Update logo
• Add logo to MultiQC report

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: https://github.com/nf-core/sarek/tree/master/.github/CONTRIBUTING.md