Bugfix: channel_mode for strobe->off, start on ramp

[readableness]

Fix channel_mode during smooth_steps operations. Maintain channel_mode until animation complete, restore ramp channel_mode before on.

Multichannel lights reverted to ramp channel_mode prior to actual off, unpleasantly mixing channels for some users during fade to off. Additionally, the ramp channel_mode would not always be restored before turning on, animating with the wrong channel_mode, then jumping to correct channel_mode at animation completion.

[readableness]

Updated commit to 4f5c8a3 to fix one more case - user interrupts off sequence/animation with a click to moon/on/turbo. This immediately restores the ramp channel_mode rather than wait to finish the turn on sequence/animation.

I believe this now covers all aspects of {strobe -> off -> ramp} that we can pull off:

• animating to off should keep last channel_mode
• EV_ticks > HOLD_TIMEOUT restores ramp channel_mode on the way to standby (possibly redundant now?)
• interrupted off sequence immediately restores ramp channel_mode on EV_click1_press