what's-new box: move the fetching of the news pages to the partial temporarily.

Otherwise, the news won’t show up when viewing the start page through
the pages controller.
blog posts: do not show the add-blog-post button in blog post detail view.

Otherwise the user might accidentally create nested blog posts.
fixing aktivitaetszahl issues.
fixing failing export spec after fixing aktivitaetszahl.
attachments: fixing behavior where the edit button has not been shown correctly. Adding first specs for document upload scenario for a closed group.
group member list export: making specs sensitive.

The specs have not been checking all list export types due to a syntax
mistake.

Always use `[‚foo‘, ‚bar‘].each { |str| … }` and do not use `for str in
[‚foo‘, ‚bar‘]`!

As a result, the specs have not been sensitive to an issue where the
birthday list could not be created due to a missing date of birth.

The spec is now fixed.
user#age: fixing the age method for users without date of birth.

This has caused problems during group member list exports.
excluding some upload specs from travis, since they do not support file uploads.
page#show: fixing an issue where the page caused an error when current_user was nil.
fixing random spec issues.