(#1874) Disable updates on non-Windows, Linux or macOS platforms (#1914)

* (#1874) Disable update checking for unsupported platforms

As described #1874, only Windows, macOS and GNU/Linux are officially
supplied with builds. Thus checking for updates is unnecessary if we
are e.g. on FreeBSD, OpenBSD, illumos distros and possibly other
Operating Systems.

This fixes #1874 by ifdef-ing the 3 officially supported platforms
when checking for updates. Otherwise a debug warning will be emitted
and in the settings the checkbox for beta-updates is hidden and
replaced by a message, explaining the reason for why there are no beta
updates.

* Update CHANGELOG

In accordance with #1874

* (#1874) Move platform check into checkForUpdates

As discussed in #1914

* (#1874) Move check for supported OS to a seperate function.

As requested in #1914

src/common/Version.hpp

@@ -11,6 +11,8 @@
 #    define CHATTERINO_OS "macos"
 #elif defined(Q_OS_LINUX)
 #    define CHATTERINO_OS "linux"
+#elif defined(Q_OS_FREEBSD)
+#    define CHATTERINO_OS "freebsd"
 #else
 #    define CHATTERINO_OS "unknown"
 #endif
@@ -26,6 +28,7 @@ public:
     const QString &commitHash() const;
     const QString &dateOfBuild() const;
     const QString &fullVersion() const;
+    const bool &isSupportedOS() const;
 
 private:
     Version();
@@ -34,6 +37,7 @@ private:
     QString commitHash_;
     QString dateOfBuild_;
     QString fullVersion_;
+    bool isSupportedOS_;
 };
 
 };  // namespace chatterino