The entity plugin should support addition of newly created entities to a persistence unit

The entity plugin just creates a new JPA entity, but it does not offer to add the newly created entity to a persistence unit. There is an underlying assumption that the PU includes unlisted classes, whereas the opposite could be true.

It is therefore desired that the entity plugin should either prompt the user to add the new entity to a PU (if there are multiple PUs), or should perhaps add the entity to an existing PU if it is the only one in the project configured to exclude unlisted classes.

Note that these are suggestions and the feature could be implemented in a suitable way to allow entities to be added to PUs.