Non-localizable control-content

### Discussed in https://github.com/perpetualKid/GetText.NET/discussions/24

<div type='discussions-op-text'>

<sup>Originally posted by **a-sanders** February 25, 2021</sup>
Hello,
It would be good to have the ability to mark some control as "non-localizable" for the Localizer (GetText.WindowsForms).

Regards.</div>