Factoring out from interpreter. DEBUGGING_MENU shows inner working.

Factored out from Menu::interpret_men_input():
bool Menu::try_page_reaction(char pg, char token);

Cleaning up debugging code, continued.
No debugging code in the example, please!

DEBUGGING_MENU is now quite usable on Arduino too.
Debugging output better formatted.

WARNING: DEBUGGING_MENU is #defined in this commit!
Shows inner menu working ;)