[MODEL] Override `ActiveRecord::Base.inspect` to prevent `ActiveRecord::ConnectionNotEstablished` errors

Rails 4 prevents these errors by default, see:

https://github.com/rails/rails/blob/v4.0.2/activerecord/lib/active_record/core.rb#L108-L122

Related: #6
[MODEL] Use `ActiveSupport#delegate` instead of stdlib's `Forwardable`

Prevent failures when `ActiveSupport#delegate` is used, e.g. in an ActiveRecord model:

    class Article < ActiveRecord::Base
      delegate :size, to: :comments, prefix: true
    end

See: http://api.rubyonrails.org/classes/Module.html#method-i-delegate

Closes #6
[MODEL] Tighten up Bundler specifications for ActiveRecord/Mongoid 3 and 4