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/util/streamlink.cpp

@@ -5,6 +5,7 @@
 #include "singletons/settingsmanager.hpp"
 #include "widgets/qualitypopup.hpp"
 
+#include <QErrorMessage>
 #include <QFileInfo>
 #include <QProcess>
 
@@ -33,6 +34,17 @@ const char *GetDefaultBinaryPath()
 #endif
 }
 
+QString getStreamlinkProgram()
+{
+    auto app = getApp();
+
+    if (app->settings->streamlinkUseCustomPath) {
+        return app->settings->streamlinkPath + "/" + GetBinaryName();
+    } else {
+        return GetBinaryName();
+    }
+}
+
 bool CheckStreamlinkPath(const QString &path)
 {
     QFileInfo fileinfo(path);
@@ -42,49 +54,57 @@ bool CheckStreamlinkPath(const QString &path)
         // throw Exception(fS("Streamlink path ({}) is invalid, file does not exist", path));
     }
 
-    if (fileinfo.isDir() || !fileinfo.isExecutable()) {
-        return false;
-    }
-
-    return true;
+    return fileinfo.isExecutable();
 }
 
-// TODO: Make streamlink binary finder smarter
-QString GetStreamlinkBinaryPath()
+void showStreamlinkNotFoundError()
 {
+    static QErrorMessage *msg = new QErrorMessage;
+
     auto app = getApp();
-
-    QString settingPath = app->settings->streamlinkPath;
-
-    QStringList paths;
-    paths << settingPath;
-    paths << GetDefaultBinaryPath();
-#ifdef _WIN32
-    paths << settingPath + "\\" + GetBinaryName();
-    paths << settingPath + "\\bin\\" + GetBinaryName();
-#else
-    paths << "/usr/local/bin/streamlink";
-    paths << "/bin/streamlink";
-#endif
-
-    for (const auto &path : paths) {
-        if (CheckStreamlinkPath(path)) {
-            return path;
-        }
+    if (app->settings->streamlinkUseCustomPath) {
+        msg->showMessage(
+            "Unable to find Streamlink executable\nMake sure your custom path is pointing "
+            "to the DIRECTORY where the streamlink executable is located");
+    } else {
+        msg->showMessage("Unable to find Streamlink executable.\nIf you have Streamlink "
+                         "installed, you might need to enable the custom path option");
     }
-
-    throw Exception("Unable to find streamlink binary. Install streamlink or set the binary path "
-                    "in the settings dialog.");
 }
 
+QProcess *createStreamlinkProcess()
+{
+    auto p = new QProcess;
+    p->setProgram(getStreamlinkProgram());
+
+    QObject::connect(p, &QProcess::errorOccurred, [=](auto err) {
+        if (err == QProcess::FailedToStart) {
+            showStreamlinkNotFoundError();
+        } else {
+            qDebug() << "Error occured: " << err;  //
+        }
+
+        p->deleteLater();
+    });
+
+    QObject::connect(p, static_cast<void (QProcess::*)(int)>(&QProcess::finished), [=](int res) {
+        p->deleteLater();  //
+    });
+
+    return p;
+}
+
+}  // namespace
+
 void GetStreamQualities(const QString &channelURL, std::function<void(QStringList)> cb)
 {
-    QString path = GetStreamlinkBinaryPath();
+    auto p = createStreamlinkProcess();
 
-    // XXX: Memory leak
-    QProcess *p = new QProcess();
-
-    QObject::connect(p, static_cast<void (QProcess::*)(int)>(&QProcess::finished), [=](int) {
+    QObject::connect(p, static_cast<void (QProcess::*)(int)>(&QProcess::finished), [=](int res) {
+        if (res != 0) {
+            qDebug() << "Got error code" << res;
+            // return;
+        }
         QString lastLine = QString(p->readAllStandardOutput());
         lastLine = lastLine.trimmed().split('\n').last().trimmed();
         if (lastLine.startsWith("Available streams: ")) {
@@ -106,17 +126,15 @@ void GetStreamQualities(const QString &channelURL, std::function<void(QStringLis
         }
     });
 
-    p->start(path, {channelURL, "--default-stream=KKona"});
-}
+    p->setArguments({channelURL, "--default-stream=KKona"});
 
-}  // namespace
+    p->start();
+}
 
 void OpenStreamlink(const QString &channelURL, const QString &quality, QStringList extraArguments)
 {
     auto app = getApp();
 
-    QString path = GetStreamlinkBinaryPath();
-
     QStringList arguments;
 
     QString additionalOptions = app->settings->streamlinkOpts.getValue();
@@ -132,7 +150,15 @@ void OpenStreamlink(const QString &channelURL, const QString &quality, QStringLi
         arguments << quality;
     }
 
-    QProcess::startDetached(path, arguments);
+    auto p = createStreamlinkProcess();
+
+    p->setArguments(arguments);
+
+    bool res = p->startDetached();
+
+    if (!res) {
+        showStreamlinkNotFoundError();
+    }
 }
 
 void Start(const QString &channel)