Remove .rvmrc

The Ruby version is set in `.ruby-version`.
Uninstall Guard

This is not used anymore.
Remove some unused and/or empty files
Uninstall Cucumber and partially implemented features
Remove obsolete submodule reference
Uninstall Capistrano and remove related files

MAGE is currently deployed via Git (à la Heroku).
Remove stale project list
Uninstall rcov

This tool has not been used in a long time. It has also not been updated since
2012 (see <https://rubygems.org/gems/rcov>).
Batch trim trailing whitespace
Remove redundant MIME types initializer
Auto-format code using RubyCop 0.28.0

Command used: `rubocop --rails --auto-correct`

Also add some RuboCop configuration and manual corrections.
Merge pull request #128 from datasektionen/vk-cleanup

Misc. cleanup