tx-browser: Create transaction browser package

[epost]

• [x] Split off from studio.
  • [x] Copy package.json from studio/ dir
  • [x] Copy spago.dhall from studio/ dir
  • [x] Copy src/Main.purs from studio/ dir to src/Statebox/Browser/Main.purs
  • [x] Copy dist from studio/ dir
  • [x] Don't hardcode example data (or indeed any of the initialState) but pass it in.
  • [x] Remove example data (the PNPRO projects).
  • [x] App title (in purple header section) should be "Statebox Transaction Browser" instead of "Statebox Studio".
  • [x] Make dir name, npm and spago project names agree.
  • [x] Merge in Sjoerd's changes to how the studio is tree-shaken and bundled.
• [x] Publish to Netlify.
  • [x] Update Netlify config to point to the transaction browser.
  • [x] Fix build breakage.
  • [x] Look into Parcel bug: https://github.com/parcel-bundler/parcel/issues/2881.
    • [x] Commit package-lock.json files.
    • [x] Duplicate all studio css files rather than depending on the common ones?
    • This fixed it for now, although it's a workaround.
    • [x] Create a separate issue for this: #352
• [x] 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?