Updates the copyright to 2021 for all files that have a copyright. Files in our source code without the copyright header still do not receive one automatically. Additionally, backlisted files are also excluded.
Previously the copyright of chiliproject which references redmine stated a copyright of redmine up to and including 2017 which is not true for the code we have in here. Because of that I changed that to 2013
This commit adds a new static helper for Links now used on more than
location in OpenProject (Homescreen + Help menu).
It allows to override the help link using the `configuration.yml`.
If it is overriden, no dropdown is rendered, but only a single link.
Ivan Kuchin