Playtime: Click only during recording

[helgoboss]

REAPER itself has checkboxes to control metronome behavior:

• Run metronome during playback
• Run metronome during recording

Of all 4 possible combinations, I think only the following ones make sense:

1. Always (playback and recording)
2. Only during recording

Also: When doing count-in recordings, the metronome should play anyway, even if the metronome is switched off.

That's why I think one simple checkbox "Click only during recording" is enough for Playtime.

See #1291.