NavigationTab{Bar,Button}: Don't mask icons by default and remove its API
Doing this is generally harmful, as it prevents the app developer from getting the icon they asked for if it happens to have any colors other than the base color. It's weird and confusing and works around icon theme issues in a way that shouldn't be encouraged. We already removed the automatic behavior in bdb32252 from Kirigami.Icon and fixed many bug reports in the process.
This commit disables the behavior and removes the API to control it.
Fixes #69 (closed)