Safe mode recovery

[Aircoookie]

Is your feature request related to a problem? Please describe.
Bootloops require complete reset of the flash contents, erasing all user settings and being a major inconvenience for controllers in hard to access areas.

Describe the solution you'd like
A safe mode that boots WLED with :

• reduced LED count
• AP mode only
  This should either be activated after a set number of unsuccessful boots (would require writing a flag to flash at every boot, not ideal for flash longevity, but can be manageable with the planned introduction of a wear levelling filesystem).
  An alternative would be checking the reset reason flag and loading safe mode if the reset was not either planned or a cold start.

[HHHartmann]

Being new to this project (but not to ESP8266) may I suggest storing the reboot count in the RTC memory?
This works great for me.

[0rsa]

+1, I just brick my Mini D1 pro updating to 12.0.0 and I have no physical access to the ESP8266. I learned a lesson :=)

[blazoncek]

power-ap branch (with power-ap usermod) features forced AP mode on 3 power cycles.
May be implemented as a core feature to either force AP mode and/or boot in safe mode.

[DedeHai]

#4793 reverts the config and even rolls-back a failed OTA. However, if there is a boot-loader mismatch, it wont help but it is probably as good as it gets.