Faster creation + QOL updates

no longer depends on gomidi/midi/v2, and now uses custom code

this allows me to only parse the data i need to, instead of reading the whole midi which was what gomidi was doing. so now it is substantially faster (enable timer in settings to check how fast)

this update also now appends the midi file if a existing midi file was given. this adds tracks straight to the midi, instead of making a copy with the edits. so now there is not an input and output option, just an output option which handles both cases

finally, the file dialog is now using the native explorer dialog instead of fyne's custom dialog. this is not only because fyne's dialog looked kind of bad, but because when choosing an existing file fyne would completely overwrite the file with empty data, which is not good. so now it only warns you of overwriting but does not change the data. allows me to actually make edits

ok thats enough rambling on, enjoy.