- Logical use of fields since they define type information.
- Avoids using ordered-dict metaclass.
Properties using regular assignments will print a warning and load,
however the order is undefined.
Fixed this with three changes:
* filter_glob is now 255 char max (63 could be a bit limited in some rare cases).
* IO templates now explicitely define max len of that property (such that scripters are aware of the limit).
* ED_fileselect_set_params() is now safe regarding too long strings from a 'filter_glob' op property.
