Added in requirement for BsbMongo Plugin

BSkyBlock will disable itself gracefully if this plugin does not exist
but the database is sent to MONGO.

Finishes up https://github.com/tastybento/bskyblock/issues/155

config.yml

@@ -49,6 +49,8 @@ general:
   ### Database-related Settings ###
   database:
     # FLATFILE, MYSQL, MONGO
+    # if you use MONGO, you must also run the BSBMongo plugin (not addon)
+    # See https://github.com/tastybento/bsbMongo/releases/
     type: FLATFILE
     host: localhost
     # Port 3306 is MySQL's default. Port 27017 is MongoDB's default.

src/main/java/us/tastybento/bskyblock/BSkyBlock.java

@@ -72,7 +72,12 @@ public class BSkyBlock extends JavaPlugin {
             getLogger().severe("Settings backup could not be saved" + e.getMessage());
         }
 
+        // Start Database managers
         playersManager = new PlayersManager(this);
+        // Check if this plugin is now disabled (due to bad database handling)
+        if (!this.isEnabled()) {
+            return;
+        }
         islandsManager = new IslandsManager(this);
         ranksManager = new RanksManager(this);
 
@@ -140,10 +145,16 @@ public class BSkyBlock extends JavaPlugin {
 
     @Override
     public void onDisable() {
-        addonsManager.disableAddons();
+        if (addonsManager != null) {
+            addonsManager.disableAddons();
+        }
         // Save data
-        playersManager.shutdown();
-        islandsManager.shutdown();
+        if (playersManager != null) {
+            playersManager.shutdown();
+        }
+        if (islandsManager != null) {
+            islandsManager.shutdown();
+        }
     }
 
     private void registerCustomCharts(){

src/main/java/us/tastybento/bskyblock/database/mongodb/MongoDBDatabase.java

@@ -10,6 +10,13 @@ public class MongoDBDatabase extends BSBDatabase{
     @Override
     public AbstractDatabaseHandler<?> getHandler(Class<?> type) {
         BSkyBlock plugin = BSkyBlock.getInstance();
+        // Check if the MongoDB plugin exists
+        if (plugin.getServer().getPluginManager().getPlugin("BsbMongo") == null) {
+            plugin.getLogger().severe("You must install BsbMongo plugin for MongoDB support!");
+            plugin.getLogger().severe("See: https://github.com/tastybento/bsbMongo/releases/");
+            plugin.getServer().getPluginManager().disablePlugin(plugin);
+            return null;
+        }
         return new MongoDBDatabaseHandler<>(plugin, type, new MongoDBDatabaseConnecter(new DatabaseConnectionSettingsImpl(
                 plugin.getSettings().getDbHost(),
                 plugin.getSettings().getDbPort(),