Add option to remove ribosomal reads

[olgabot]

Addresses #74 to remove ribosomal reads from the trimmed sequences, so that down the line the differential hash expression doesn't even have the option of looking at ribosomal abundance, which is usually more related to sequencing depth than biological function.

PR checklist

• PR is to dev rather than master
• 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/kmermaid 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

[olgabot]

Docker is currently building so all the tests are failing because sortMeRNA is not installed.