release-electron-3.0.0

1. New Feature: The entire code has been refactored to support the extensible architecture. For details on extension development, please refer to our official website. Let's make Paperlib better together!
2. New Feature: Hierarchy Folders and SmartFilters!
3. New Feature: All metadata scrapers and downloaders have been moved into corresponding extensions.
4. New Feature: A new command panel interface has been introduced to replace the basic search bar.
5. New Feature: Support for creating new tags and folders in the sidebar.
6. New Feature: Changable table view column order and more columns.
7. New Feature: SmartFilter can be edited after creation. Add more human-friendly labels for SmartFilter creation.
8. Others: Fixed some bugs.
9. Others: Doesn't support Windows 7 anymore.