add library support for settings menu

[Neumi]

write methods for an universal 7-segment and button input menu to change parameters that get stored in EEPROM.

it has to:

• be easy to use
• be easy to adapt for other use cases
• save data in EEPROM and read on start
• should be controlled using the three button inputs

the menu could have a tree structure like this: -> baud -> 2400 -> 4800 -> 9600 -> rs485 -> 1 -> 0

see the temperature controller example.