do remote library update in a different thread

Put updateRemoteLibrary in a new thread so it doesn't block the main UI, particularly the loader widget

src/contentmanager.cpp

@@ -18,6 +18,7 @@
 #include "contentmanagerdelegate.h"
 #include "node.h"
 #include "kiwixconfirmbox.h"
+#include <QtConcurrent/QtConcurrentRun>
 
 ContentManager::ContentManager(Library* library, kiwix::Downloader* downloader, QObject *parent)
     : QObject(parent),
@@ -539,11 +540,13 @@ void ContentManager::updateLibrary() {
 
 #define CATALOG_URL "library.kiwix.org"
 void ContentManager::updateRemoteLibrary(const QString& content) {
-    m_remoteLibrary = kiwix::Library();
-    kiwix::Manager manager(&m_remoteLibrary);
-    manager.readOpds(content.toStdString(), CATALOG_URL);
-    emit(this->booksChanged());
-    emit(this->pendingRequest(false));
+    QtConcurrent::run([=]() {
+        m_remoteLibrary = kiwix::Library();
+        kiwix::Manager manager(&m_remoteLibrary);
+        manager.readOpds(content.toStdString(), CATALOG_URL);
+        emit(this->booksChanged());
+        emit(this->pendingRequest(false));
+    });
 }
 
 void ContentManager::setSearch(const QString &search)