When setting options that have a NULL value by default (such as imageFieldName) the setConfig function would incorrectly assume the option was not available and would silently ignore.
This fix implements a correct option validation mechanism, and throws an error if an incorrect option assignment is attempted.
All bulk edit tools will now use "bulk-edit-tools" HTML fragment,
defined in base component GridFieldBulkEditingTools. Previous
"GridFieldBulkEditingTools" is now GridFieldBulkEditingHelper.
Component now finds the Image relation and all 'editable fields' itself.
Also gets the edit Forms from the record's getCMSFields()
+ other little fixes