util.with_lock: add support for chaining with @event_listener

Consider e.g.:
```
class AddressSynchronizer(Logger, EventListener):
[... snip ...]
    @event_listener
    @with_lock
    def on_event_blockchain_updated(self, *args):
        self._get_balance_cache = {}  # invalidate cache
        self.db.put('stored_height', self.get_local_height())
```

was raising:
```
func.__qualname__='with_lock.<locals>.func_wrapper'
Traceback (most recent call last):
  File "...\electrum\run_electrum", line 105, in <module>
    from electrum.logging import get_logger, configure_logging  # import logging submodule first
  File "...\electrum\electrum\__init__.py", line 19, in <module>
    from .wallet import Wallet
  File "...\electrum\electrum\wallet.py", line 70, in <module>
    from .address_synchronizer import (
  File "...\electrum\electrum\address_synchronizer.py", line 75, in <module>
    class AddressSynchronizer(Logger, EventListener):
  File "...\electrum\electrum\address_synchronizer.py", line 205, in AddressSynchronizer
    def on_event_blockchain_updated(self, *args):
  File "...\electrum\electrum\util.py", line 2005, in event_listener
    classname, method_name = func.__qualname__.split('.')
ValueError: too many values to unpack (expected 2)
```

electrum/util.py

@@ -1243,6 +1243,7 @@ def ignore_exceptions(func):
 
 def with_lock(func):
     """Decorator to enforce a lock on a function call."""
+    @functools.wraps(func)
     def func_wrapper(self, *args, **kwargs):
         with self.lock:
             return func(self, *args, **kwargs)