change matrix pattern more often

Trying to have a number of pattern which are not dividable by
the number of calls. This ensures a somewhat random switch.

- call new function nextMatrixPattern()
- display random pattern on 7 segment less long
add sleep mode after some pattern cycles

- sleep mode is IDLE, since no other mode is possible by the setup
- timer 1 triggers wakeup after approx. 30s
- all other timers and interrupts are switched off during the time
set doxygen to quiet mode

- enable all warnings, though