Allow parameterization of new window creation

This commit adds a new parameter to the window manager's create() method. It is
passed on to the method actually creating the requested window. This parameter
allows to get data into the otherwise isolated window creation process. However,
a window creating method doesn't need to make use of this.

This functionality may be used if a widget should be cloned.
Neuron navigator: add button to duplicate widget

The button is placed in the upper right corner of the navigator widget. When
clicked, it will instruct the window manager to create a new window, based on
a new navigator instance it created. The current node will be deep-copied and
will therefore clone all it's parents. All new nodes are then linked to the new
navigator and the current one is selected.
Neuron navigator: fix some style issues and typos