add option of disable auto update

app/src/main/java/com/hippo/ehviewer/ui/MainActivity.java

@@ -331,7 +331,9 @@ public final class MainActivity extends StageActivity
 
         if (savedInstanceState == null) {
             onInit();
-            CommonOperations.checkUpdate(this, false);
+            if (Settings.getAutoCheckUpdateEnable()) {
+                CommonOperations.checkUpdate(this, false);
+            }
             checkDownloadLocation();
             if (Settings.getCellularNetworkWarning()) {
                 checkCellularNetwork();