load kwarg traits before loading config...
load kwarg traits before loading config
in `Configurable.__init__`
avoids problems in the new init of traitlets
that skips `_trait_default` if specified in kwargs,
which means really nothing should be done before `HasTraits.__init__` has been called.
This does mean that such values are assigned twice.
Typically, this will have no effect,
except when a value is set by both config and kwarg.
