Adapt modules to the nf-core structure

[JoseEspinosa]

Description of feature

Adapt local modules to the nf-core structure:

module_name
├── environment.yml
├── main.nf
├── meta.yml
└── tests
    ├── main.nf.test
    ├── main.nf.test.snap
    └── tags.yml

The dir tests shouldn't be there if tests are not implemented yet.

[JoseEspinosa]

Closed in favor of #194