Toolbar #149

similar to bokeh's tool buttons, automatically append this to the bottom of any plot, unless tool_buttons=False or something. Could use icons for it, can get free icons here: thenounproject.com

For all plot areas:

• auto scale
• center scene
• checkable button for maintain aspect
• enable/disable pan zoom controller, once this is merged: Cameras and controller overhaul pygfx/pygfx#457
• flip camera.scale.y, https://fontawesome.com/icons/rotate?f=classic&s=solid
• record start & stop once this is merged: basic recording for Plot #178
  • just save in the nb local path for now, use timestamp for filename
• add selectors (once they are ready) adding selectors with buttons doesn't make much sense, can wait until we have right-click menus for those since those are really specific to a parent graphic.
• tooltip for all buttons

ImageWidget specific:

• reset vmin vmax - for ImageWidget, can use a contrast icon
• Play button, try out the ipywidgets play, stop, pause etc. stuff again
• step size, BoundedIntText widget