Consider combining required and type validator

[mokkabonna]

It can be a bit verbose now.

The required validator is now mainly there for avoiding programatically setting the value to undefined.

If the required validator also validated the type then it would be fewer validators.

I any case all validators should only kick in if the type validator passes. This creates an overlap that causes 2 errors to be shown unnecessarily. Currently it only requires the required validator to pass.