* documentation and script updates trying to fix#1647
* preparations for refactoring target/bin/
* complete refactor for target/bin/
* changing script output slightly
* outsourcing functions in `bin-helper.sh`
* re-wrote linting to allow for proper shellcheck -x execution
* show explanation for shellcheck ignore
* adding some more information
Moved variable VIRUSMAILS_DELETE_DELAY to Dockerfile. This variable will be written to /etc/environment in the start
script to make it visible to cron. Also removed echo in cron job to prevent sending mail for each run.
