Indicate when the device is sleeping vs awake

[ThomasFarstrike]

Currently, the user has no indication of whether the device is awake or sleeping, as the ePaper display stays "on" during sleep.
Especially on the new LilyGo T5 ePaper 2.13 inch devices, as they have no LEDs that show it being powered on.

It would be useful to indicate sleep vs awake to the user because if it's awake, it might be draining battery, and it might give instant feedback if a payment is received, while if it's sleeping, it needs to be woken up to refresh etc.

During sleep, the wifi signal strenght on the display ("Wifi: XX%" in bottom right corner) is completely stale and useless, because the device is not even connected to the wifi during sleep.

So it would be good to replace the wifi signal strength on the display with a sleep indication, such as "ZZzz..." or "ZzZz..." or "zzZZ" or "SLEEP". This can probably be triggered from the hibernate() function in Main/WakeupAndSleep.ino

[ThomasFarstrike]

Work ongoing at https://github.com/LightningPiggy/lightning-piggy/tree/issue-3-indicate-sleeping

[ThomasFarstrike]

This is done, again with a bit of rework to clear parts of the display before redrawing, as the device doesn't always go to sleep anymore.

[ThomasFarstrike]

This is ready and deployed in v2.0.0 in the webinstaller.