Add and update bootloader and a fix for up_n_down

The biggest part is a cleanup of the bootloader. I was able to reduce the size considerably. I am currently using the extra space for the __MONITOR__ feature, but others may implement other features (or get more space for the main program). Either way, I simply want to share this optimization with everybody.

There is one additional commit to `up_n_down.ino`. After 5 clicks, it doesn't turn off (glow mode was disabled). To be honest, I am not quite sure how DPIN_PWR got activated, but the MCU was definitely still running after I locked the light with 5 clicks.