[myank] preserve *staff, *part, and *group lines in extracted measures

[craigsapp]

When myank extracts measures after the first (or zeroth for pickups), it removes *staff, *part and *group information. This breaks display of the !!!system-decoration, so preserve it.

Also consider preserving instrument names and abbreviations (or just abbreviations).

[craigsapp]

And optionally add an option to add empty names such as *I" and *I'.