[Power] Add extra display page showing power consumption

[TD-er]

Since I have been busy with the AXP192 on this T-beam 1.0 board, I thought why not adding a separate display showing the actual power state.

Power page showing discharge current

Power page showing charge current

Power page showing no charge, but with USB connected

As the display is updated quite often, I had to apply some basic filtering on the USB power stats or else it was hardly readable since the values fluctuate quite a lot.

[cyberman54]

Thanks for this PR (and the other one). I will look at this soon, test & merge.

[TD-er]

@cyberman54 I just tested with this in the beginning of the setup() function:

  // Reduce power consumption
  setCpuFrequencyMhz(80);

This reduces the power consumption with about 50 mWatt.
Typically it uses 660 mWatt when the CPU freq. is set to 80 MHz.
When left running at 240 mHz, the power consumption is about 710 - 730 mWatt.

I'm also making the screen layout for this power display page a bit more readable, including the power consumption (or power used for charging)

[TD-er]

Running from battery:

Charging from USB:

Will append the commit for it in a minute

[cyberman54]

make power consumption optional, because main purpose of paxcounter is wifi/ble sniffing, affording high cpu speed