Tears of Steel

New features and a bunch of under-the-hood improvements!

• subtitle file loader now opens the media asset directory by default
• audio visualizations support
• a .desktop file was added, along with an appstream and logo files
• many small but relevant UI-related bug fixes
• overall code-base revamp leading to circular-ref-cycles and memory leak fixes

Many thanks to the new contributors, @thiblahute @alatiera and @tathanhdinh !