Polkassembly integration improvements

[rzadp]

Listing improvements that did not make it in the first PR introducing this integration.

• More logs - #79 (comment)
• More robust way to determine the referendum ID - #79 (comment)
• Comment on a PR with feedback from the Polkassembly integration (a link to the referendum on success, or information about error)
  • Decided to scratch this one at this time - we already have a matrix message about a new tip, and we can check logs about Polkassembly integration after that.
• Have a prettier / more expressive description on Polkassembly. We're no longer keeping things short because we no longer store this on-chain