Revamp overall report UI and improve report navigation

[myanvoos]

This PR overhauls the overall report UI (layout and template/sample pages) and adds a few improvements including:

• A dark mode theme for all three pages
• Navigation breadcrumbs
• Toggle-able table of content for the index page (located top right of the screen)
• Dedicated header showing aggregated results for the index and benchmark pages
• A function to create a unified JSON file out of experimental results that preserves the hierarchical relationships between projects, benchmarks, and samples

[DavidKorczynski]

Could you post screenshots?

IMO on thing that we should watch out for is losing overview ability for the benefit of more modern-looking UI. Following #1062 I think it's more difficult to traverse the benchmarks on a higher level, probably because we have significantly reduced the amount of benchmarks shown on the screen at once. I find when experiments have hundreds of benchmarks it's convenient to have a lot of data shown at once.