Missing the ability to add uncertainty to reference to entity

[bug-rancher]

As in the topic - in Annotator's interface it is not possible to add uncertainty to reference to entity. This ability is described in article: https://docs.google.com/document/d/1shETwBiKcRGdfsIY2L60FLQUmT0XqSescFnbOaDEiQs in section 5.9.