Layout Improvement. Compile in 1.6. TreatControlEnabledFalseAsNull option

- layout : use a GridbagLayout instead of Border Layout, added a ScrollPane too.
- TreatControlEnabledFalseAsNull option : changed the logic for determining if "null value" should apply. 
It works better on the case I tested:
    Having set TreatControlEnabledFalseAsNull = true in the options, I expect disabled components (eg. Date Editor) to return null, but enabled components should return a value (was not the case before this change)
Did I miss something ?
- compile in 1.6