Explode & Implode

Adds native explode & implode functions to a new "Tools" submenu under "Edit". 

Explode: select a range on either a single staff or a group of staves.  The top staff of the selection is treated as the source.  All chords within the range on the source staff are exploded into the remaining staves in the selection.  If user selected only the source staff, then the function uses as many staves as it needs.

Implode: select a range on a group of staves.  The top staff of the selection is treated as the destination.  All chords within the range on the destination staff are augmented by the notes of chords on the same segment on the other staves.

These functions only behave well if the material lends itself to explosion / implosion - a series of chords in a single voice per staff with the same rhythm.  Notes that do not fit this model are simply ignored.  While it's a pretty simple algorithm, it is actually a pretty big improvement over the plugins for 1.3.  For explode, you don't have to copy the source to the other staves first, and chords with fewer notes than there are staves are handled better (each note of the chord is duplicated as necessary).  For implode, it handles tuplets and ties, and tries to avoid duplicate notes.