Bluetooth module: fetch battery percentage from upower if not found from bluez

[levnikmyskin]

What is this PR about?

Current bluetooth module shows battery percentage from bluez experimental features. This has two drawbacks:

1. Not super user friendly, as users need to activate these features;
2. Most importantly, a lot of devices (at least in my experience) do not report battery percentage anyway, despite having it in upower;

Upower implementation

In this PR, the bluetooth module will first try to fetch battery percentage from bluez and, if not available, will try fetching it from upower.

Other details

At the moment, the code is getting all upower devices, and then looking for the one with the correct serial number. I don't know if there's a better way of doing this

[levnikmyskin]

Thank you for your suggestions, implemented :)

[levnikmyskin]

Hi @Alexays, is there anything missing here or could we merge this? thanks :)