Introduce StateManager to persist state between power cycles (#6)

- add reset state menu option to return all settings back to default values.
- add reverse encoder menu option and save state
- make saving to EEPROM safer by wrapping put calls with noInterrupts()
- improve save state behavior by using a mutex flag and update check with debounce in main loop
- refactor gravity.h global const definitions to be static and more readable.
- improve usage of EncoderDir in ISR with pointer to instance and static isr() method.
- reduce u8g2 memory usage by using single page buffer

Reviewed-on: https://git.pinkduck.xyz/adam/libGravity/pulls/6
Co-authored-by: Adam Wonak <adam.wonak@gmail.com>
Co-committed-by: Adam Wonak <adam.wonak@gmail.com>

peripherials.h

@@ -39,6 +39,4 @@
 #define OUT_CH5 9
 #define OUT_CH6 11
 
-const uint8_t OUTPUT_COUNT = 6;
-
 #endif