Move to panel-material-ui

[SebastianHambura]

Move to Panel Material UI: https://panel-material-ui.holoviz.org/

Pros:

• cleaner, modern look
• Should be easier to theme
• Some new widgets out of the box (like the Tree)
• Some new Menu and possible interactivity things

Cons:

• Need to change quite some code left and right
• Currently a bit unstable: sometimes changes trigger an error (see: Cannot read properties of undefined (reading 'top_panel') panel-extensions/panel-material-ui#548 ) - and the tabulator also don't update 100% of the times
• Theming is now another pseudo-language (ie. mui specific).
• By default, all the stuff is quite spaced out, so the whole app is less compact

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Working branch: https://github.com/prevedel-lab/BrimView/tree/pmui