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.
after removing font unit:
```
set_if('fontSize', shape.getFontSize().getValue())
AttributeError: 'NoneType' object has no attribute 'getValue'
```

sorry about confusion