add optional argument to method

• for easy retrieve of info.yml value like website (documentation_link)
• defaults to null, so the default behavior is not broken
add convenience method for documentation link

• like this simple the link and the link_title can be passed as argument
• the button will always be displayed at the same location
Add example documentation_link to dashboard

• using new convenience method in info_bar widget
• passing link value as a request parameter value