Tribler/tribler: V7.5.2

This is a minor release with a heavy focus on bug fixes. We have addressed most of the issues reported in Tribler 7.5.1 and plan to fix the remaining issues in our next release.

Important changes:

• Updated Python interpreter to Python 3.8
• Disabled embedded VLC video player due to compatibility problems
• Updated Libtorrent version to 1.2.4 in Windows builds and fixed compatibility with Libtorrent 1.2.4+ in Unix versions
• Stopped fetching empty Channels from remote peers

<details> <summary>Full changelog</summary> * Disable video play buttons * Add Mock in versionchecker tests * Add timeout in async version check * Update version check interval to six hours * Add release url in the version check manager * Fix RemoteQuery not using model properties * Remove fault handler from pip3 requirements.txt * Update run instruction in README file * Fix Pony unique transaction error * Using SelectorEventLoop in the Windows tests * Fix mdblob squash test failing randomly * Not starting libtorrent session in download tests * Ported GUI tests to pytest * Fix add to channel error * Broke testnet settings into multiple ones * Totally ignore gaierrors * Fixed GUI test event loop policy * Ignoring gaierror with errno -5 * Switched Win64 GUI test to SelectorEventLoop * Updated IPv8 pointer * Simplified Windows dev documentation * Using SelectorEventLoop by default * Removed too informative logging statements * Added Windows batch script to start Tribler * Removed cp65001 code * Fixed SHOW_CONSOLE variable * Removed built-in libraries from dependency checker * Fixed dependency checker when starting Tribler * Updated Windows development env docs * Disable VLC loading * Let unhandled_error_observer deal with gaierrors * Check for new version immediately after starting * Merge pull request #5487 from qstokkink/add_lt1.1.13_support * Added libtorrent 1.1.13 support for listen_succeeded_alert * Make GUI send last traceback on core timeout error * Shutdown ResourceMonitor during unit tests * Skip profiler test if Yappi is not installed * Fix libtorrent 1.2.4+ compatibility * Add default download path to recently used dirs cache * Fix a minor comma issue in Debian control file * Add build parameters on snap build script * Made VLC a recommended dependency * Fixed BUILD_TRIBLER_SNAP variable check * Removed ffmpeg * Updated Linux requirements * Updated Debian building documentation * Added more info to OverflowError * Updated IPv8 pointer * Removed unicode string prefix from TriblerTunnelCommunity * Remove introduction point circuits from slots * Update IPv8 pointer * Fix gossiping zero-sized channels * Merge pull request #5448 from devos50/shutdown_bootstrap * Shutting down Bootstrap before IPv8 * Fix wrong table update * Ask user for channel name on creation * Workaround for channels table racecon * Fix channels table uid remapping on removal * Fix error on adding magnet to collection * Fix wrong index in tablecontentmodel * Fix double model reset * Fixed loading VLC libraries on Windows * Update snap base to core20 from core18 * Added fix for tribler.spec with latest setuptools * Merge pull request #5423 from egbertbouman/various_fixes * Fix TorrentDef.get_files_with_length * Make debug panel work with latest IPv8 * Speedup tunnel tests + remove tests that check for tunnels not working * Show task name when event loop is dirty * Fix RESTManager shutdown * Fix UDPTracker and fix test_check_torrent_health * Fix loops and extra lines in trust balance graph * Period tracker check changes * Updated IPv8 pointer * Delaying video player initialization * Removed Twisted tutorial * Removed Python 2.7 pyinstaller support * Fixed test_error_observer_ignored_error * Fixed peer count limit for RemoteQueryCommunity in debug panel * Pathlib fix for profiler endpoint * Handle CancelledError in download_channel * Don't wait for the DHT while doing tunnel tests * Fix TorrentDef.get_name_as_unicode </details>