Improve emailing for data models

• A log for both validation and linting should be generated and archived.
• The result of both runs should be part of the email sent.
• It would be good if for the –3gpp run the messages related to the changed YANG modules would be highlighted.
• The author is directly responsible for those, but not necessarily for messages related to other modules.

Sadly there might be a big number of messages for existing modules about non-critical problems e.g. too long lines or use of tab characters.