Add tx2gene module (formerly local to rnaseq)

[pinin4fjords]

nf-core/test-datasets#1083 should be merged first, and appropriate adjustments made here.

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 module conventions in the contribution docs
• If necessary, include test data in your PR.
• Remove all TODO statements.
• Emit the versions.yml file.
• Follow the naming conventions.
• Follow the parameters requirements.
• Follow the input/output options guidelines.
• Add a resource label
• Use BioConda and BioContainers if possible to fulfil software requirements.
• Ensure that the test works with either Docker / Singularity. Conda CI tests can be quite flaky:
  • PROFILE=docker pytest --tag <MODULE> --symlink --keep-workflow-wd --git-aware
  • PROFILE=singularity pytest --tag <MODULE> --symlink --keep-workflow-wd --git-aware
  • PROFILE=conda pytest --tag <MODULE> --symlink --keep-workflow-wd --git-aware

[adamrtalbot]

Want me to wait for nf-core/test-datasets#1083 before reviewing?

[pinin4fjords]

Want me to wait for nf-core/test-datasets#1083 before reviewing?

No, go right ahead. I'll update the test data reference, but everything else should be good

[adamrtalbot]

I don't like how the error is handled, but since this is a port I think we should go with it and add an additional test in future.