Incoming deprecations

Summary

• Subhandler data storage
• Entso_e.py line 592: now = datetime.utcnow()

Explain your context

(Explain what you did.)

What is the expected correct behavior? What was your goal?

(What you should see instead.)

What is the current bug behavior?

(What actually happens.)

Was there an error message?

test/test_connectors/test_modbus.py::TestConnectorSubscriptions::test_subscribe
d:\ETA\eta-utility\eta_utility\connectors\sub_handlers.py:513: FutureWarning: Setting an item of incompatible dtype is deprecated and will 
raise an error in a future version of pandas. Value '' has dtype incompatible with float64, please explicitly cast to a compatible dtype 
first.
self._data.loc[timestamp, node.name] = value

to format console output, logs, and code, as it's very hard to read otherwise.)

Steps to reproduce

(How one can reproduce the issue - this is very important)