Manage disconnected & timeout errors

[gonzamontiel]

When the node disconnects, or it's connected but not producing blocks, the site fails silently. This ticket is about:

• [ ] Detecting that the node is disconnected
• [ ] Detecting that the node is not producing blocks (this might be challenging, can be handled with sending a tx and adding a timeout to the response)
• [ ] Besides the node name (under Pendulum logo), show a green dot when the node is connected, and a red dot when is not. Might include the connected and disconnected wordings.

[erasmus]

WebApp deprecated soon. Closing.