No more update prefs on the first run.
Adjust code indent
Remove obsolete codes.
Centralize APIs to common.js.
Centralize string APIs.
Move preferences to "extensions.scrapbook.addon.maf.*"
Fix: wrong datetime when converting a folder.
Fix: sub-folders cannot be added to the .maff correctly.
Fix: Supress error messages by no-folder items (eg. separators) when making maffs from a folder.
Fix: Check existence for the output file and do not check existence for recursive files when merging multiple items into one.
Update version info.