- `Fetch` and `Rebuild database` will work more safely.
- Case-sensitive renaming now works fine.
Revoked the logic which was made at #130, however, looks fine now.
- Now periodic internal file scanning works well.
- The handler of Window-visibility-changed has been fixed.
- And minor fixes possibly included.
Refactored:
- Unused logic has been removed.
- Some utility functions have been moved into suitable files.
- Function names have been renamed.
