Description

Improves and updates the linting procedures.

1. Bumped linter versions to their latest release as of today.
2. Streamlined test/linting/lint.sh
3. Added new configuration file for ECLint
4. Had to update start-mailserver and setup-stack.sh as ShellCheck was complaining with v0.7.2. So I revised SPAMASSASIN_SPAM_TO_INBOX_SET for the better and removed the ugly sub-shell usage which was totally unnecessary.

Fixes #1997

Type of change

• Improvement (non-breaking change that does improve existing functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (README.md or the documentation under docs/)
• If necessary I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

PS: I got the PR marked with #2000 🎉