Fix: avoid start lag

Prevent the first light going "down" from off (=0) to 0, first cycle is
now "up" from 0 to 1000
Short press prevention

Avoid to turn on if button is not held pressed
Fix button declaration

Worked just because button_pressed is false (=0), replaced by test to
test if button is released.
Fix button declaration

Was not working. Button test replaced: if button held for more than
200ms: go back to fade mode.