Make sample names header-like

[fhausmann]

Description of changes

The DRIMSEQ filtering pipeline is not running, when sample names contain special characters, due to automatic conversion. This automatic conversion is now applied also to the sample names.
This should fix #129, #140, #165.

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 you've added a new tool - have you followed the pipeline conventions in the contribution docs
• If necessary, also make a PR on the nf-core/rnasplice branch on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core lint).
• Ensure the test suite passes (nextflow run . -profile test,docker --outdir <OUTDIR>).
• Check for unexpected warnings in debug mode (nextflow run . -profile debug,test,docker --outdir <OUTDIR>).
• Usage Documentation in docs/usage.md is updated.
• Output Documentation in docs/output.md is updated.
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).

[lpantano]

@fhausmann do you want to update this to see if tests get triggered and we can merge?

[fhausmann]

@lpantano I'm happy to update/work on this more if needed. However, I'm not sure what kind of update is required. As far as I can see, there are no merge conflicts. What updates are required?