update TODO
make attributes validate() external values

removes the need to sync entered data from view/binding to
model/attribute just to validate it
add unparseable number as validation error type
add convenience constructor to DataException
DataAttributes: convert types before validation

throw ValidationError when conversion is impossible
also reuse the code for conversion on setValue()
Glue: run UI validations on view values

no need to call syncToModel on every attribute, do the validation on the
model value and revert the model value afterwards
fix NPE on wrong filetype

ImageIO.read() throws no Exception, but returns null :-/
FileBinding: also mark the JTextField on validation error
move ValidationError display code from Glue to Binding