The basic idea is that when a link doesn’t specify the value for a query
param, the current value is preserved. 

So, given the hierarchy

```
qps // defines a QP named “string”
  qps.details // defines a QP named “nestedString”
    qps.details.more // defines a QP named “doubleNestedString”
```

Links inside `qps.details.more` that point to `qps.details` will contain
“nestedString=bar&string=foo”, but never “doubleNestedString”.
Links inside `qps.details` that point to `qps` will contain “string=foo”,
but never “nestedString” or “doubleNestedString”.
Links inside `qps.details` that point to `qps.details` with a different
will model will contain “string=foo” but never “nestedString” or “doubleNestedString”.
Links from a route to any descendant route will always include all the 
query params defined in the path.