Improve Spanish Translation

[antoniojturel]

Thank you for submitting a Pull Request to the Mobile Application Security Verification Standard. Please make sure that:

• [ ] Your PR is linked to an issue.
• [ ] Your PR follows the contribution guidelines
• [ ] All links are valid and use HTTPS and have been formatted as [TEXT](URL “NAME”)
• [ ] In case of a translation: have you made sure that the translation from EN is as close to the EN document as possible?

This PR closes #643.

If your pull-request has a focus of rewriting a requirement and/or adding a new one, please make sure you have a backing issue in which your change has been discussed and agreed. If there is none, then your PR will be closed without further review.

[antoniojturel]

This PR is a full in depth review of 13 files, It wasn´t easy but effective step by step, great job @cpholguera !