META Gnoweb improvements

[moul]

Random ideas for improving the portal loop (#1108):

• gnoweb: include the block height in the footer. #1214
• Enhance error handling by displaying errors within the theme instead of causing panic.
• Implement a maintenance mode for when the node is starting.
• Create a page that lists the latest N contracts.
• Add a form to execute arbitrary data for contracts using q_exec.
• Show the contract publisher in the footer.
• Display the date/height of the most recent state modification for the current realm.
• Improve the help generation based on @thehowl's work with gno doc.
• Embed the docs/ folder in the interface (gno.land/docs/) and include the result of go doc somewhere. This way, you can run gnoland locally and have all the necessary documentation to work independently.
• Make it easier to detect a localnet/testnet/special net; perhaps with customizable logo color, etc.
• This is not a complete list...