tx-browser: loose ends

[wires]

There are a couple of small-ish changes that should be make to the browser:

• [x] have the focus of the tree be part of the URL
• [x] update the URL when a hash is pasted
• [x] navigation doesn't work, should be removed
• [x] the left sidebar looks strange without any context, should be hidden in that case
• [x] no need to input a PNPRO file here
• [ ] API base URL should probably be chosen from a fixed set of URLs