Do not show finished Ideas in the Ideenspeicher

even though the idea was updated more than seven days ago they should
not appear in the archive
fixes #15
add scope methods to Idea model for finished and not_finished
Add Changelog
format changelog
Merge pull request #20 from okfde/15-complete-projects

Startseite: Abgeschlossene Projekte nicht im Ideenspeicher
Change name of admin user
Merge branch 'master' into 16-voting
Add changelog to PR