Reset Parity Ethereum light client node blockchain data when block synchronisation fails

[ltfschoen]

I was just trying to send a transaction with Fether, and I thought the Kovan network may have been down, but then I noticed that it wasn't syncing blocks (i.e. it wasn't showing Imported #....) logs in the terminal. This may have been caused because I was switching between different chains.

If a user runs Fether with a built-in Parity Ethereum node in either development or production, and it stops syncing blocks, at the moment the FAQ doesn't make it clear what they should do.

They might find the FAQ "Where is the light client blockchain data used by Fether stored?" https://wiki.parity.io/Fether-FAQ#where-is-the-light-client-blockchain-data-used-by-fether-stored, and then try deleting the chain data for the network that wasn't syncing

rm -rf $HOME/.local/share/io.parity.ethereum/chains_light/kovan

But if the user was running a separate Parity Ethereum node whilst running Fether, and they were familiar with the CLI, they'd find they could use the CLI to purge the chain:

./target/debug/parity db kill --chain [your chain]
parity db kill --chain [your chain]

Or just search for the process ID that was running a Rust build and kill it:

ps aux | grep ./target/debug | awk 'NR==1{print $2}' | sudo xargs kill -9;

I think we should add an option to the Fether menu that purges/resets the chain data that they're currently running (i.e. Fether menu > Help > Reset Chain Database), and add another question to the Fether FAQ "How to reset the light client blockchain data used by Fether?" that explains to the user how they can do it from the Fether menu or manually, and another question "Why isn't Fether syncing?" that links to that question.