tx-browser: Create transaction browser package

[epost]

• Split off from studio.
  • Copy package.json from studio/ dir
  • Copy spago.dhall from studio/ dir
  • Copy src/Main.purs from studio/ dir to src/Statebox/Browser/Main.purs
  • Copy dist from studio/ dir
  • Don't hardcode example data (or indeed any of the initialState) but pass it in.
  • Remove example data (the PNPRO projects).
  • App title (in purple header section) should be "Statebox Transaction Browser" instead of "Statebox Studio".
  • Make dir name, npm and spago project names agree.
  • Merge in Sjoerd's changes to how the studio is tree-shaken and bundled.
• Publish to Netlify.
  • Update Netlify config to point to the transaction browser.
  • Fix build breakage.
    • Look into Parcel bug: parcel-bundler/parcel#2881.
      • Commit package-lock.json files.
      • Duplicate all studio css files rather than depending on the common ones?
        • This fixed it for now, although it's a workaround.
      • Create a separate issue for this: #352
• After merging Sjoerd's studio bundling PR, move studio/src/Main.purs to studio/src/Statebox/Studio/Main.purs or something? NB: This might be invasive wrt pending branches/PRs.
• Update docs site; 'explorer' should be 'transaction browser'.
• Update github milestone and project names.
• Update dev meeting template link titles.
• Retroactively add links to meeting notes for discoverability?