Add SKIP_POW_DIFFICULTY_VALIDATION flag to AbstractNet for chains using custom difficulty algorithms like LWMA. Update blockchain.py to skip pow validation when flag is set, relying on server validation and checkpoints instead. Also update Palladium checkpoints.
Add initial configuration files for Palladium chain including servers, checkpoints, and fallback nodes.
Update constants to use Palladium as default network and rename PalladiumMainnet to Palladium for consistency.
Adds the mutinynet signet (https://github.com/MutinyWallet/mutiny-net/)
to the supported networks so it's possible to
use it with Electrum. Mutinynet is similar to signet, except for a
shorter block interval (30 sec), a nice faucet
(faucet.mutinynet.com) and some extra features in its core fork.
It also has some lightning network nodes, see
the mempool instance on mutinynet.com.
note: I find "chains" less ambiguous than "networks" or "net".
Though the codebase already uses "net"/"network" for the same meaning,
e.g. see `electrum.constants.net` or the `getinfo` cmd dict containing a "network" key.. :/
