Add build comparison tab

[oboking]

An initial way to address:
#8817
#7816
#4402

Description of the problem being solved:

I myself always end up with one PoB application for my actual imported character from the game, and one window for the goal PoB I'm going for, and its quite annoying to juggle both applications and spot the differences between the PoB's if you don't know what you are missing.

There are many ways the feature could be improved (for example overlaying trees, better explanations for the sources of the stats in the calcs tab, key differences across tabs in the summary tab, colored gems in the skills tab etc) but I think it serves most of my needs pretty good.

Video of feature:

showcase.mp4

I would love to hear your guys input on it 😄

[Wires77]

I'll have to play with it once the league start work calms down. Just from the gif you need a ConfigSet dropdown too. You could use the Tree comparison feature in that tab to make direct comparison easier. Not sure how that ends up looking with different jewels and such, though.

We've previously been hesitant to add something like this because of performance concerns, but if this just compares the XML it might be okay.