Improve reading md5 from REMARK lines

[joaomcteixeira]

You are about to submit a new Pull Request. Before continuing make sure you read the contributing guidelines and you comply with the following criteria:

• You have stick to Python. Talk with us before adding other programming languages to HADDOCK3
• Your PR is about CNS
• Your code is well documented: proper docstrings and explanatory comments for those tricky parts
• You structured the code into small functions as much as possible. You can use classes if there's a (state) purpose
• code follows our coding style
• You wrote tests for the new code
• tox tests pass. Run tox command inside the repository folder
• -test.cfg examples execute without errors. Inside examples/ run python run_tests.py -b
• PR does not add any install dependencies unless permission granted by the HADDOCK team
• PR does not break licensing
• Your PR is about writing documentation for already existing code 🔥
• Your PR is about writing tests for already existing code

---

The original implementation for reading md5 hashes from REMARK lines was loose and caused errors in some structures with more complex REMARK lines. This PR corrects this behaviour by adding a robust checking and reading of md5 hashes and assigning them to MODELs.

Previous tests pass.

scoring examples are currently broken because of this bug.

Related to #459

[mgiulini]

looks good!

[joaomcteixeira]

Thanks for the review @mgiulini. I am merging because this is a critical bug. We can address any additional comments in the future weeks if needed.
Cheers,

[mgiulini]

@joaomcteixeira no problem, I think it's more than fine for the time being!