Make each axis in axes_manager.gui() its own Accordion

[thomasaarholt]

Currently the axes_manager.gui() consists of ipywidgets.HBox([nav_accordion, sig_accordion]). As an example, nav_accordion is one accordion wrapped around a list of the axes widgets.

Each accordion can only have one open tab at a time. This means that one can't quickly hop between navigating in x and then in y.

It would be better to make each axis an accordion, then put the navigation ones and the signal ones in separate ipywidgets.Boxes, and then HBox the two boxes.

[thomasaarholt]

Example image, where opening Axis 1 closes Axis 0.