Replaces reform by a simple layer of Disposable +
ActiveModel::Validations for contracts.
Additionally removes the custom error handling where OpenProject added
symbols to keep the ability to identify faulty attributes while having
non standard format (deviates from `%{attribute} %{message}`).
Changes to active record now allow us to define the format of a message
on i18n level, e.g. `%{message}`. Therefore the patching can be removed.
Reform plans to remove support for ActiveModel::Validations in version
4.0 at the latest but even today, support for it is hapazard. As we do
not need the full stack of Reform anyway, we can solely rely on
Disposable.
Alexander Brandon Coles