fix #402 no tag form in note_card/project

現状annotationがembedしているオブジェクトとしてcardの派生クラスであるstateを指定した場合に、以下のようなエラーが出ているのですが、解決の方法するためには何を指定すべきか教えてください。

Failure/Error: annotation = FactoryGirl.create :annotation, annotatable: state
     Mongoid::Errors::InvalidPath:

       Problem:
         Having a root path assigned for Card::Annotation is invalid.
       Summary:
         Mongoid has two different path objects for determining the location of a document in the database, Root and Embedded. This error is raised when an embedded document somehow gets a root path assigned.
       Resolution:
         Most likely your embedded model, Card::Annotation is also referenced via a has_many from a root document in another collection. Double check the relation definitions and fix any instances where embedded documents are improperly referenced from other collections.