Extend "explode" and "implode" to support multiple voices

actually the tools explode and implode only support voice #1.
It would be fine to extend their functionality to support also several voices:
- explode: look if there is more than one voice in the selected staffs. If so, create as much note lines as the maximum number of voices. If only one voice, work identical as now. (If there are chords with more than one note per voice, keep them in together - if the user wants to split them, too, he can do it in a second call of the tool).
-implode: extend to collect all voices that appear in the selected staffs. If a user wants to collect the note lines in separate voices he needs to change the voice number before calling "Implode". So he can decide how the imploded notes will appear in the collected note line.