Child theme route overwrite

[jlambe]

Child theme routes are overwritten by the parent theme.

We should provide a check that if a route is already registered regarding a child theme, this route can't overwritten by the parent theme.

Note: check against plugins routes as well.

Route hierarchy:

1. Plugin route
2. Theme route (has precedence over a plugin route)
3. Child theme route (has precedence over a parent theme route)