Update FilterFieldGenerator.java

In some cases I need to know name of property to create proper filtering field otherwise I am not able to create it for a specific property which isn't listed as container property id  - getContainerPropertyIds (for example: column generated based on some other properties - state icon, etc.)
Merge pull request #34 from qavid/patch-1

Provides the property name for field generator even when the property is not found in the container (e.g. generated columns)