Update to @material-ui/core@4.12.2

[cmdcolin]

This PR updates to @material-ui/core, lab, and data-grid, presumably getting bugfixes and improvements. I was actually interested in this though because I used jb2export and it printed the message

$ jb2export --fasta ~/src/gmod/jbrowse/docs/tutorial/data_files/volvox.fa --configtracks refseq --loc ctgA:1-100

Material-UI: the createMuiTheme function was renamed to createTheme.

You should use `import { createTheme } from '@material-ui/core/styles'`

This is somewhat interesting just because it shows we are getting an updated @material-ui/core when installing it with npm install -g @jbrowse/img. That makes sense because we don't necessarily pin versions

I tried updating to the latest @material-ui/core just to make sure that generally things work, in case this affects things like @jbrowse/linear-genome-view.

I did see an issue with upgrading where the accordion panels were transparent so I fixed that and upgraded the deps

[codecov]

Codecov Report

Merging #2141 (61a4023) into main (c2aa053) will increase coverage by 0.02%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main    #2141      +/-   ##
==========================================
+ Coverage   61.95%   61.98%   +0.02%     
==========================================
  Files         476      476              
  Lines       22763    22763              
  Branches     5344     5344              
==========================================
+ Hits        14103    14109       +6     
+ Misses       8379     8373       -6     
  Partials      281      281              

Impacted Files	Coverage Δ
...kages/core/BaseFeatureWidget/BaseFeatureDetail.tsx	76.25% <ø> (ø)
packages/core/ui/DrawerWidget.js	94.28% <ø> (ø)
packages/core/ui/DropDownMenu.tsx	100.00% <ø> (ø)
packages/core/ui/ViewContainer.tsx	80.55% <ø> (ø)
packages/core/util/io/ElectronLocalFile.ts	3.33% <0.00%> (ø)
...r-view/src/CircularView/components/CircularView.js	90.90% <ø> (ø)
...ConfigurationEditorWidget/components/SlotEditor.js	63.82% <ø> (ø)
...lot-view/src/DotplotView/components/ImportForm.tsx	76.92% <ø> (ø)
...omparative-view/src/LinearComparativeView/model.ts	9.47% <ø> (ø)
...ew/src/LinearSyntenyView/components/ImportForm.tsx	0.00% <ø> (ø)
... and 15 more

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