Рефакторинг, очистка, работа над ошибками, связанными с базой, отказ от глобальной переменной $user во многих файлах.

Singleton в некоторых местах вместо решения #42.
Новые шаги для решения #16 и #52.
Closes #42.
Closes #32.
Closes #31.

classes/Battles/UserStats.php

@@ -3,7 +3,7 @@
 
 namespace Battles;
 
-use Battles\Database\DBPDO;
+use Battles\Database\Db;
 use Exceptions\GameException;
 
 class UserStats extends User
@@ -86,7 +86,7 @@ class UserStats extends User
             throw new GameException(self::ERROR_STAT_IS_MAXIMUM);
         } else {
             $query = "UPDATE users SET {$stat_name} = {$stat_name} + 1, free_stat_points = free_stat_points - 1 WHERE id = ?";
-            self::$db->execute($query, $this->id);
+            Db::getInstance()->execute($query, $this->id);
         }
     }
 
@@ -161,7 +161,7 @@ class UserStats extends User
 
     public function getFullStats(): object
     {
-        $stats = self::$db->ofetch("
+        $stats = Db::getInstance()->ofetch("
         select
                strength,
                dexterity,
@@ -170,7 +170,7 @@ class UserStats extends User
                intelligence,
                wisdom
         from users where id = $this->id");
-        $itemBonuses = self::$db->ofetch("
+        $itemBonuses = Db::getInstance()->ofetch("
         select
                sum(add_strength) as item_strength,
                sum(add_dexterity) as item_dexterity,
@@ -184,7 +184,7 @@ class UserStats extends User
                sum(add_min_physical_damage) as item_min_physical_damage,
                sum(add_max_physical_damage) as item_max_physical_damage
         from inventory where dressed_slot != 0 and owner_id = $this->id");
-        $effectBonuses = self::$db->ofetch("
+        $effectBonuses = Db::getInstance()->ofetch("
         select
                sum(mod_strength) as effect_strength,
                sum(mod_dexterity) as effect_dexterity,
@@ -238,6 +238,6 @@ class UserStats extends User
             $this->level,
             $this->id //where
         ];
-        DBPDO::$db->execute($query, $vals);
+        Db::getInstance()->execute($query, $vals);
     }
 }