The new view lists the appropriate model entities and provides the ability to create and assign
unique attributes to them. The format is simular to the Attribute View with the following additional
view attributes:

- Type = "ModelEntity"
  * - Col1Header - The name to be used as the column 1 header if the attribute
  * does not exist "Model Entity" is displayed
  * - Col2Header - The name to be used as the column 2 header if the attribute
  * does not exist "Type" is displayed
  * - NoValueLabel - The label to be used to indicate that a model entity does not have an appropriate attribute associated with it

This commit also includes changing attributes() method that return attribute UUIDs to attributeIDs() and
added a new EntityRef::attributes(attribute::DefininitionPtr def) that returns the attribute are based on
def (or derived from it)

Also made qtBaseView a friend of the qUIManager so derived views have access to invokeEntitiesSelected method