Abstract FavoritesCollection.basePath(), for use in migration and FilesView.
Implement migrator for file names containing "%". Not yet hooked up, though.

Using cordova "fileEntry.moveTo()" or "fileEntry.copyTo()" fails with
FileError.INVALID_MODIFICATION_ERR trying to move (or copy) from, eg,
character%3Acolon.txt to character%253Acolon.txt. The move (or copy)
works fine for target name XXXcharacter%3Acolon.txt. Weird.