Remove position computations, use MUI components and new splitter

[WardBrian]

I initially intended only to address #71 (comment), but maintaining our current layout quickly led me to use some more MUI components and remove the absolute positioning. Apologies for the monolithic PR

• Uses a 3rd party splitter, closes Fix odd rendering when splitter dragged to the top #71
• Removes computed sizes/absolute positioning, closes Consolidate inline styling to CSS classes. #23 and Replace absolute positioning with alternative #24
• Uses MUI for buttons and other UI elements, closes Use MUI buttons throughout #22
• Simplifies main component chain, removes a lot of unnecessary divs and CSS, closes Simplify main-content component chain #78

My goal was not to change any layouts or functionality, though some visual features have changed, mostly due to using MUI more

[jsoules]

Couple possible tweaks. Overall I think it looks good, but will want to take a deeper look on Monday.

[magland]

Overall this looks good to me. I think the top bar takes up too much vertical space now.

This causes challenging conflicts with #127 (and maybe #132 as well). I started to look at it but it wasn't going smoothly. How do you propose we deal with that? Since those involve tab widgets, I think it would have been better if we had merged those first. Do you think it's reasonable to merge those and then apply the changes of this PR? Or other way around?

[WardBrian]

Yeah, I realized as I was going it would cause some conflicts going either way. I am willing to do the merge resolution on whichever one doesn’t go first, but I don’t have a strong opinion on the ordering there

[magland]

I am willing to do the merge resolution on whichever one doesn’t go first

That would be great if you are willing to do that, because I was getting confused in my attempt. :)

[magland]

I tested this out and I think the changes all look good, except IMO the title bar has too much vertical space.

[WardBrian]

@magland -- I've updated the top bar to use MUI's dense variant, which trimmed a lot of the padding:

Before:

After:

[magland]

Okay I think it's still too big, but it's not a huge deal and I wouldn't want to block the merge.

[jsoules]

I don't think I have anything further on this, if you're happy with it.