working on your_platform.

* moving several components from wingolfsplattform to your_platform.
* creating basic setup which creates an admin user.

trello: https://trello.com/c/KUdRePRv/683-yourplatform-setup
what's-new box

* show only pages that concern the current user: selection by groups
rather than just cancan.
* change box title to „what’s new in my groups“
* sort by „updated_at“ rather than „created_at“.
* updated_at is touched on the page when new attachment is uploaded.
what's-new box: fixing issue where the pages variable is nil.
local admins: adding spec to avoid caching issues.