revert: "refactor(core): Remove unused Core::reset method"

This reverts commit 4664c6249a.

src/core/core.cpp

@@ -1435,3 +1435,18 @@ void Core::killTimers(bool onlyStop)
         toxTimer = nullptr;
     }
 }
+
+/**
+ * @brief Reinitialized the core.
+ * @warning Must be called from the Core thread, with the GUI thread ready to process events.
+ */
+void Core::reset()
+{
+    assert(QThread::currentThread() == coreThread);
+    QByteArray toxsave = getToxSaveData();
+    ready = false;
+    killTimers(true);
+    deadifyTox();
+    GUI::clearContacts();
+    start(toxsave);
+}

src/core/core.h

@@ -78,6 +78,7 @@ public:
 
 public slots:
     void start(const QByteArray& savedata);
+    void reset();
     void process();
     void bootstrapDht();