Fix: signal/slot macro -> func pointer & network fixes

- convert qt connect calls to use function pointers instead of the signal/slot macros wherever practical (UI classes were mostly left alone, target was tasks and processes)
- give signals an explicit receivers to use the static method over the instance method wherever practical
- ensure networks tasks are using the `errorOccured` signal added in Qt5.15 over the deprecated `error` signal
- ensure all networks tasks have an sslErrors signal connected
- add seemingly missing `MinecraftAccount::authSucceeded` connection for `MSAInteractive` login flow

Signed-off-by: Rachel Powers <508861+Ryex@users.noreply.github.com>

launcher/ui/pages/instance/VersionPage.cpp

@@ -501,7 +501,7 @@ void VersionPage::on_actionDownload_All_triggered()
         return;
     }
     ProgressDialog tDialog(this);
-    connect(updateTask.get(), SIGNAL(failed(QString)), SLOT(onGameUpdateError(QString)));
+    connect(updateTask.get(), &Task::failed, this, &VersionPage::onGameUpdateError);
     // FIXME: unused return value
     tDialog.execWithTask(updateTask.get());
     updateButtons();