Move patches location

[alecandido]

This should close #126.

To do:

• change the path in the code to the internal one
• scope mg5 paths inside the mg5 subpackage (cuts_code, cuts_variables, and patches)
• ❌ update the relative docs -> there was little before, nothing to update

[alecandido]

@cschwan there are a lot of changes, but most of the files changed are only because of whitespaces normalization, so you will simply skip.

The main content of the PR is in the title: it moves patches folder from top-level to mg5 package, and it adjust paths in order to correctly point to the new location (plus it moves mg5 specific paths into a module in its subpackage).

[alecandido]

P.S.: note that in a first instance pre-commit normalized even patches, and for this reason they were not working any longer. They are now excluded from normalization:
https://github.com/NNPDF/runcards/blob/0b1f2a56f292a029ac4db384a232f31da53d32b1/.pre-commit-config.yaml#L3

However, if you manually run pre-commit run --all-files it will affect even patches, so in case pay attention to restore them (or not to stage).