Fix bug in `Showable.get_result` that prevented it from returning a v…

…alue if

`Showable.get_future` had not previously been called.
Add testing notebooks.
Move debugging notebooks down a level.

Update 'cubevis.min.js' libraries for the remaining, supported Bokeh …

…versions

[colab eval_js cleanup] debugging eval_js in colab notebook (0010)

                        python logging is a pain

[colab eval_js cleanup] debugging eval_js in colab notebook (0008)

                        update documentation

[colab eval_js cleanup] debugging eval_js in colab notebook (0007)

                        increment debug notebooks

[colab eval_js cleanup] debugging eval_js in colab notebook (0009)

                        remove diagnostic output (01)

[colab eval_js cleanup] debugging eval_js in colab notebook (0008)

                        update documentation

[colab eval_js cleanup] debugging eval_js in colab notebook (0007)

                        increment debug notebooks

[colab eval_js cleanup] debugging eval_js in colab notebook (0006)

                        using a single name for the chunking BroadcastChannel results
                        in the chunks being collected by all of the anywidget bridges
                        This change creates a chunking BroadcastChannel that is named
                        based on `_comm_mgr_id`

[colab eval_js cleanup] debugging eval_js in colab notebook (0006)

                        using a single name for the chunking BroadcastChannel results
                        in the chunks being collected by all of the anywidget bridges
                        This change creates a chunking BroadcastChannel that is named
                        based on `_comm_mgr_id`