Fix feature labels being choppy by downgrading react 18 to react 17

[cmdcolin]

I noticed on react 18 that the "floating feature labels" (feature label stays shown on left side of screen while scrolling feature) would look "choppy" when side scrolling the app.

It appears to be due to using react 18. This could be due to any number of reasons but react does say that it "interupts" rendering with react 18. We can still "support" react 18 but the floating feature labels look less smooth in it, so our "apps" might want to stay on react 17. I upgraded to react 18 in the mui5 branch, but it appears it will be better to stay on react 17 for now.

• smooth, v1.7.11, react 17 - https://jbrowse.org/code/jb2/v1.7.11/?config=test_data%2Fvolvox%2Fconfig.json&session=share-HqBaavoxQW&password=GqRKf
• choppy, main, react 18 - https://jbrowse.org/code/jb2/main/?config=test_data%2Fvolvox%2Fconfig.json&session=share-HqBaavoxQW&password=GqRKf
• smooth, this branch, react 17 - https://jbrowse.org/code/jb2/fix_floating_labels/?config=test_data%2Fvolvox%2Fconfig.json&session=share-HqBaavoxQW&password=GqRKf