remove broken website field from profile

Websites can be added with markdown in the blurb field
remove groups websites
replace github contributing links → wikia link
clean code from websites

Need review !
migration script: websites → blurb
Merge pull request #1795 from Fandekasp/remove_website

remove broken website field from profile
[#923] also migrate group.websites => group.description (@Fandekasp the
user stuff is solid, thanks!)
Merge pull request #1811 from Fandekasp/update_contrib_link

replace github contributing links → wikia link