terms of use.
restructure app/model/abilities. no changes in behaviour.
changing member list export rights.

           - BV-Mitgliedschaft berechtigt dazu, die Mitglieder dieses BV
               zu exportieren.
           - Mitgliedschaft in einer Verbindung als Bursch oder Philister
               berechtigt dazu, die Mitglieder dieser Verbindung zu
               exportieren.
           - Normale Gruppen-Mitgliedschaften (etwa Gruppe 'Jeder'
               oder 'Wingolfsblätter-Abonnenten') berechtigen nicht zum
               Export.

trello: https://trello.com/c/1UqSsBHx/681-neue-rechte
fixing caching issue 'undefined method created_at'.
fixing security issues using brakeman.

there have been 2 vulnerabilities concerning possibly unsafe use of
`constantize`.

trello: https://trello.com/c/owV5FC2M/584-brakeman-check
fixing feature specs to include the terms of use.

trello: https://trello.com/c/gbEQHjJZ/682-nutzungsbedingungen
working on new rights.

* attachments can have authors, now.
* officers can create pages in their domains
* they can edit their own pages
* they can upload attachments
* they can edit and destroy their attachments

trello: https://trello.com/c/1UqSsBHx/681-neue-rechte
groups#show: making authorization more efficient.

Using the cancan `accessible_by` scope is faster than looping over all
objects and calling `can?` separately. But, in order to make it work,
we could not use a block for `can :read, User` anymore.
using rspec-rerun to rerun failing capybara tests, especially on travis.

https://github.com/dblock/rspec-rerun
fixing Rakefile after introducing rspec-rerun.
configure travis for rspec-rerun.
fixing BlogPostController

* use new abilities: https://trello.com/c/1UqSsBHx/681-neue-rechte
* fixing behaviour when adding a new blog post via ajax.
what's new: increasing number of news entries.
rspec-rerun: adding file `rspec.failures` to `.gitignore`.
excluding strangely failing spec from travis.
update authorization info

* officers box
* restricted pages

trello: https://trello.com/c/1UqSsBHx/681-neue-rechte
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