vcf2maf module created
Additions:
- vcf2maf module created
- If VEP is present in PATH, it is added to command
- If VEP is missing, it is ignored (recommended to skip with --inhibit-vep)
- VEP version automatically added to versions.yml
- Uses VEP cache during testing which is added to test-datasets in https://github.com/nf-core/test-datasets/pull/563
- Default Docker image includes VEP and vcf2maf
- Test includes without VEP.
Relates to #490
