Make a demo-sleep-clock.cpp example

[martinberlin]

Simple example to make an epaper clock that will initially make a request to internet to get the time. And then will update every N minutes refreshing the epaper display.
The objective of this is just to make an additional epaper demo and have some fun along the way. By no means this will be a precise clock!

1. If is 00 hours or there is a IO button low force internet sync time
2. Wakeup and increment the clock. Render super fast updating only that part of the epaper
3. Keep hour / minute in the EPROM
4. Go to deepsleep N minutes -> Repeat 1

1 day sprint. Max 2 days including release. Pending list:

• Add zero padding to digits <9 - Wrong should be of course when <10
• Add internet internet time sync with https://github.com/martinberlin/cale-api
• Add partial refresh to this display test model ( Gdew027w3 )
• Correct leading 0s in updateClock() since is <9

[martinberlin]

Add a state text in case it cannot connect to the Internet.
It should keep on working and just mark the hour as updated leaving a message "Could not connect to WiFI" only till next refresh.

[martinberlin]

It's done and so far working as a wristwatch since months. The connect to internet still happens to block it, will add it later but it was just a demo so it's not high priority. Thanks for all the attention on this one!