corrected virtual member functions for derived classes in Menu.hh

some corrections, does not change anything in the binary.
some problems in the settings menu with cursor exists.

I build mighty_twox: .
I tested with avr-g++-4.9.0 with the same libc, it works fine, but it is not for distribution as there some differences in sizes.

text      data    bss
124929 1270  5522     avr-g++-4.6.2
107974 1006  5522     avr-g++-4.9.0