Add brief description to Streamlink settings page

Add links to Streamlink website and download page to Streamlink settings page
Make streamlink custom path usage more explicit
Change how streamlink runs, it now works perfectly on Linux so that if you don't have a custom path set, it will try to just run "streamlink" in your PATH variable

This needs testing on Windows again

src/singletons/settingsmanager.hpp

@@ -61,10 +61,6 @@ public:
         "/behaviour/autocompletion/onlyFetchChattersForSmallerStreamers", true};
     IntSetting smallStreamerLimit = {"/behaviour/autocompletion/smallStreamerLimit", 1000};
 
-    // Streamlink
-    QStringSetting streamlinkPath = {"/behaviour/streamlink/path", ""};
-    QStringSetting preferredQuality = {"/behaviour/streamlink/quality", "Choose"};
-    QStringSetting streamlinkOpts = {"/behaviour/streamlink/options", ""};
     BoolSetting pauseChatHover = {"/behaviour/pauseChatHover", false};
 
     /// Commands
@@ -114,6 +110,13 @@ public:
 
     BoolSetting inlineWhispers = {"/whispers/enableInlineWhispers", true};
 
+    /// External tools
+    // Streamlink
+    BoolSetting streamlinkUseCustomPath = {"/external/streamlink/useCustomPath", false};
+    QStringSetting streamlinkPath = {"/external/streamlink/customPath", ""};
+    QStringSetting preferredQuality = {"/external/streamlink/quality", "Choose"};
+    QStringSetting streamlinkOpts = {"/external/streamlink/options", ""};
+
     void updateWordTypeMask();
 
     void saveSnapshot();