Various improvements (#264)

- Replace C function pointers with C++ `std::function` in `Thread`, `Timer` and `DispatcherThread`
- Rename `SystemEvent`-related functions
- WiFi: fix auto-connect when WiFi disconnects from bad signal
- WiFi: fix auto-connect when WiFi fails to auto-connect
- WiFi: implement disconnect() when tapping connected WiFi ap in WiFi management app

Tactility/Source/app/wifimanage/View.cpp

@@ -69,7 +69,13 @@ static void connect(lv_event_t* event) {
     if (ssid != nullptr) {
         TT_LOG_I(TAG, "Clicked AP: %s", ssid);
         auto* bindings = (Bindings*)lv_event_get_user_data(event);
-        bindings->onConnectSsid(ssid);
+
+        std::string connection_target = service::wifi::getConnectionTarget();
+        if (connection_target == ssid) {
+            bindings->onDisconnect();
+        } else {
+            bindings->onConnectSsid(ssid);
+        }
     }
 }