Multi-Scene Support

This release adds support for multi-scene files! When napari-aicsimageio reads a multi-scene image it will pop open a widget with a list of all scenes in that file as well as some options for how to load those scenes.

This feature is marked as experimental so please give it a go and give us feedback! If reception is positive we are even considering making this the default loading pattern for napari-aicsimageio so that the user can set even more parameters before loading with options like #28 and #29.

Major thanks to @psobolewskiPhD for the large majority of this work, to @tlambert03, @jwindhager, and @Czaki for being readily available for questions, and to the napari community as a whole. This was a lot of work and feedback from a lot of people.