Add fit button to network visualization

[vincerubinetti]

Currently, you can double click the network visualization to fit the view to contents. But not everyone will know to do that. Let's add a "fit" button with these buttons:

Will need to find an appropriate icon that is distinct from the "fullscreen" button. The tooltip for the button should be something like "Fit view to contents (or double-click viz)".

[kemsguy7]

Kindly assign this to me

[kemsguy7]

@vincerubinetti , please kindly review