Tests: entity changed after form submit + fix

When I submit form in a component, data are not passed to entity.
This fix it + add test.


### Results for Travis:

Failing test: https://travis-ci.org/Kdyby/DoctrineForms/builds/39269681
It's fix: https://travis-ci.org/Kdyby/DoctrineForms/builds/39270259

Looks like this was introduced in Nette 2.3, since both passes 2.2.

---

This partly depends on #12, where tests are fixed.