Tribler 7.0.0

What's new in this version:

- Tribler 7 is one of our biggest releases so far and has been in development for almost two years. Since the latest release, we made a total of 2,055 commits and changed 1,070 files (with 80,073 additions and 99,227 deletions). We closed over 400 issues on our Github repository, fixed hundreds of bugs and made major improvements to the user interface and torrent downloading mechanism. We added a blockchain fabric to Tribler to accurately keep track of bandwidth contributions on a dedicated page in the user interface. This innovation allows us to build new features to make Tribler more stable, faster and secure to use.

Changelog:
- Redesigned the user interface and dropped wxPython in favor of PyQt
- Made a clean separation between the user interface and the Tribler core. This significantly improves speed and stability
- Deployed a blockchain fabric within Tribler to keep track of bandwidth contributions
- Added new RESTful API for developers
- Created a twistd plugin, allowing users to run Tribler without a user interface
- Refactored our test suite significantly. Unit tests execute faster now and are more reliable
- Improved the build process of the Tribler executable on Windows and macOS
- Updated dependencies of Tribler to the latest versions
- Fixed compatibility with latest versions of libtorrent
- Improved integration of the Twisted framework with the Tribler codebase
- Executables on Windows are now signed
- Fixed many race conditions due to context switches between various threads
- Improved error reporting functionality when Tribler crashes
- Improved the debug panel and expanded it with additional information
- Fixed various memory leaks when running Tribler for several hours or days
- Improved Unicode support
- Fixed various bugs when receiving malformed packets from other peers