[Cpuchain-dev] Activating signet with minimal difficulty

We should skip testnet and activate signet, because it is better than testnet. Or, we could fix testnet bugs, for example "blockstorm bug", and then activate it. I think that signet with minimal difficulty 0x7fff...f will be enough for all test cases, because now mainnet difficulty is still quite close to minimal difficulty, so to test things quick, we should lower it, because then producing a lot of test blocks will be possible. Also, signing blocks will protect us from attacks. And to allow other users playing with signet coins, we could create some faucets.