Add dbd --convert-dave option

Enables metadata conversion from DAVE's AppleDouble format to Netatalk.
Add function loadvolinfo()_path. Add --volinfo arg and don't open the CNID db.

o delete DAVE ressources that can't be opened
o delete nested .AppleDouble directories from inside DAVE resource.frk dirs
o remove orphaned DAVE resources
o use --volinfo=PATH arg for specifying a .volinfo file
o when running --convert-dave don't open the CNID db
o remove a few options