Save placeholder on ToTextField

[LANDAISB]

1. I add ToTextField on a pyramid project
2. I set placeholder on a textfield: OK,
3. I save and close pyramid
4. I open pyramid again: placeholder is nil

[Nyan11]

This issue is a serialization issue.
It should be fix in https://github.com/OpenSmock/Toplo-Serialization

[MagueresMathieu]

fix in OpenSmock/Toplo-Serialization#26