Move session logging code to protocol.py from electrum_rpc.py
Use it for periodic logging controlled by envvar LOG_SESSIONS
For each session, track sent transaction stats and show that
per-session instead of errors
Daemon URLs can be comma-separated in the DAEMON_URL env var.
Surrounding whitespace is stripped.
http:// is preprended if missing.
The coin's default port is supplied if missing.
A trailing / is supplied if missing.
Closes#33
