[BUG] Cubeviz: Spectrum viewer toolbar won't close when using slice slider

[PatrickOgle]

Describe the bug There is no direct way to close the spectrum viewer toolbar when using the cube slice slider. This is a problem because it obscures the wavelength readout. It is also more generally a problem because it obscures the spectrum plot. Current untenable workaround is to select the display options menu then click elsewhere to make that go away.

To Reproduce Steps to reproduce the behavior:

1. Launch cubeviz from jupyter notebook
2. Load data cube into viewers
3. Open toolbar and select cube slice slider tool
4. See error

Expected behavior Click elsewhere, eg. header, to make toolbar disappear OR... reinstate 'X' tool to make toolbar disappear AND move wavelength readout somewhere it isn't in the way AND move toolbar up so it doesn't obscure the plot.

Screenshots Attached.

Desktop (please complete the following information):

• OS: macOS-10.15.7
• Browser: Firefox
• Jupyter: [run "jupyter --version"]

jupyter core : 4.6.3 jupyter-notebook : 6.0.3 qtconsole : 4.7.4 ipython : 7.14.0 ipykernel : 5.3.0 jupyter client : 6.1.11 jupyter lab : 3.2.9 nbconvert : 6.0.7 ipywidgets : 7.6.5 nbformat : 5.0.6 traitlets : 5.0.5

Package versions (please complete the following information):

macOS-10.15.7-x86_64-i386-64bit Python 3.8.2 | packaged by conda-forge | (default, Apr 24 2020, 07:56:27) [Clang 9.0.1 ] Numpy 1.20.3 astropy 4.3.1 specutils 1.6.0 pyyaml 5.4.1 click 7.1.2 asteval 0.9.23 idna 2.10 traitlets 5.0.5 bqplot 0.12.33 bqplot-image-gl 1.4.5 glue-core 1.2.2 glue-jupyter 0.10.1 glue-astronomy 0.3.2 echo 0.5 ipyvue 1.7.0 ipyvuetify 1.8.1 ipysplitpanes 0.1.0 ipygoldenlayout 0.3.0 voila 0.2.6 vispy 0.6.6 Jdaviz 2.2.1.dev183+gc523362f

Additional context (e.g. data files) Add any other context about the problem here.

[PatrickOgle]

Moving the toolbar to the left of the tools button would solve the problem in the short term.