Images inserted in scores behave as embedded, rather than as linked (as before).

I.e.: images keep the contents they had when inserted, ignoring modifications (or deletion) of the original source image.

Note: this applies only to .mscz files; images in .mscx files must to rely on the external source, as there is no resource actually included in the score.
Merge pull request #501 from mgavioli/Images_as_embedded

Truly embedded images (vs. linked)
Fix the crash when (copying/cutting and) pasting a single lyrics to a single note.
Merge pull request #502 from mgavioli/Single_lyrics_paste

Single lyrics paste