[CLI] investigate potential multi-threading issues

[PiRK]

When using Cash Fusion in command line mode, we sometimes see warnings about functions not being called from the "main thread". This is likely not an issue, as there is no main GUI thread running in CLI mode and everything is handled by the daemon process which receives commands via RPC calls, but it should be investigated nonetheless, and if it turns out to be safe the warning should not be printed.

On load_wallet:
/tmp/.mount_ElectrODAFm6/usr/lib/python3.8/site-packages/electroncash/storage.py:255: UserWarning: run_hook "get_action" being called from outside the main thread (thr: Thread-3) may lead to undefined behavior. Please use util.do_in_main_thread to call run_hook if the hook in question does not return any results

We also see similar warnings when a fusion happens and the software adds a label to the transaction.