refactor: Toast (#4899)

* Fixes a bug where avatars weren't loaded on fresh installations of Chatterino.
* Avatars now update every two weeks.
* Removes misleading `DownlaodManager` (now part of `Toasts.cpp`).
* Refactors usage of WinToast to be easier to read.
* Added version to AUMI.
* Removes manual `QString` → `std::wstring` conversions.
* Removes uses of implicit ASCII casts in `Toasts.cpp`, meaning it can be compiled with `QT_NO_CAST_FROM_ASCII`.

src/CMakeLists.txt

@@ -26,8 +26,6 @@ set(SOURCE_FILES
         common/ChatterSet.hpp
         common/Credentials.cpp
         common/Credentials.hpp
-        common/DownloadManager.cpp
-        common/DownloadManager.hpp
         common/Env.cpp
         common/Env.hpp
         common/LinkParser.cpp