Remove etc/license_header.txt

This file is not in use.
doc: Add chapter IDs to authentication.md
doc: Add section 'Database Setup' to authentication.md

fixes #7672
doc: Remove developer information from preferences.md
Make command parameters with multiple lines work, again

fixes #6088
Hide unsupported export formats

refs #8112
Clarify that php-gd is mandatory to export views to PDF

refs #8112
Merge branch 'bugfix/hide-unsupported-export-formats-8112'

fixes #8112
puppet: Add note to the icingacli module that it's not reuseable
puppet: Add user 'vagrant' to group 'icingaweb'
lib: Fix PHPDoc of Form::setOnSuccess()
lib: Add separator parameter to String::cname()
monitoring: Remove css class 'control-group' from the expire time element

This CSS class does no longer exist.
monitoring: Remove css class 'control-group' from date and time elements in the schedule downtime command form

This CSS class does no longer exist.
Add module-aware Form::translate and Form::translatePlural

refs #7551
Use the class namespace instead of the request in Form::translate(Plural)

refs #7551
Do NOT fetch the translation domain from the request in Form::translate(..)

It might be the case that a module is using a library form...

refs #7551
Fix incorrect token generation example on the wizard's welcome page

fixes #8135
Fix the config warning's grammar on the login screen
There is no copy-on-write for objects in PHP

fixes #8088