Ignore units on FontSize in shapeMarshall

This fixes an issue reported by @aleksandra-tarkowska where text label ROIs break ROI display in web (due to font size units). https://github.com/openmicroscopy/openmicroscopy/pull/3245#issuecomment-65805182

To test, add a text label Shape to an image in Insight, then test that it displays in web.
When I removed fontsize from the DB there is an issue with a query
```
serverExceptionClass = ome.conditions.InternalException
    message =  Wrapped Exception: (org.springframework.orm.hibernate3.HibernateSystemException):
Null value was assigned to a property of primitive type setter of ome.model.units.Length.value; nested exception is org.hibernate.PropertyAccessException: Null value was assigned to a property of primitive type setter of ome.model.units.Length.value
``` 
I think keeping it as it is should be fine