Connecting to a electrum backend via Tor

It'd not yet possible to connect to a electrum via Tor. We basically need something very similiar than `specter.requests_session`:

```
def requests_session(self, force_tor=False):
requests_session = requests.Session()
if self.only_tor or force_tor:
proxy_url = self.proxy_url
proxy_parsed_url = urlparse(self.proxy_url)
proxy_url = proxy_parsed_url._replace(
netloc="{}:{}@{}".format(
str(random.randint(10000, 0x7FFFFFFF)),
"random",
proxy_parsed_url.netloc,
)
).geturl()
requests_session.proxies["http"] = proxy_url
requests_session.proxies["https"] = proxy_url
return requests_session

```