Make MultiTextInput more general

[Remi-Gau]

At the moment this component is hard coded to deal only with only 3 fields:

• first name
• middle name
• family name

Suggestion: make those the defaults placeholder to keep backward compatibility (though I could only identify one item in the reproschema library that uses it) but allow for the possibility to create new inputTypes by just changing the place holder passed to that component.