Add column property in the version table

[AbdealiLoKo]

polymorphic_on supports column_property() defined on the mapper.
But the version mapper does not have the column property making it fail even though the mapper_args are being copied into the version table.

This also makes it more natural for the user - because they can directly access column properties from the version table itself

This also copies the column_property() into the version tables

Relates to #297

[AbdealiLoKo]

Right now - I have impleented this assuming all column properties should be copied - cause I thought that would be useful.
But if you think this is not a good idea, I can add the column property only if a column property is being used in the polymorphic_on

Also - @marksteward I was not sure whether this should be in builder.py or model_builder.py
I saw the mapper args were being added in model_builder.py but column-properties and relationships are being added in builder.py
I feel like this should be in model_builder.py

[AbdealiLoKo]

@marksteward this one is blocking me from using continuum too

Does next-release mean next major or minor or patch release ?