security fix for CVE-2014-0130.

trello: https://trello.com/c/0TcN1TSF/602-security-cve-2014-0130.

further reference: https://groups.google.com/forum/\#\!topic/rubyonrails-security/NkKc7vTW70o
updating devise due to security issue '2014-05-07 CSRF TOKEN FIXATION ATTACKS'.
update to ruby version 2.1.2.

release info: https://www.ruby-lang.org/en/news/2014/05/09/ruby-2-1-2-is-released/
trello: https://trello.com/c/PySEkLOD/615-update-auf-ruby-2-1-2
replacing rmagick gem by mini_magick gem.

* https://github.com/carrierwaveuploader/carrierwave\#adding-versions
* https://trello.com/c/dQn0NeXp/616-rmagick-minimagick
fixing AttachmentUploader#cover filter.
fixing workflow_kit gem to version 0.0.7 until migrating to rails 4.

workflow_kit 0.0.8 only supports rails 4.
merging current master into rails4 topic branch in order to have the ruby 2.1.2 update in.