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.