Prevent copy & move of abstract classes

To prevent slicing, following C++ Core Guidelines C.21 and C.67.

cpp/include/loot/database_interface.h

@@ -39,8 +39,15 @@ namespace loot {
 /** @brief The interface provided by API's database handle. */
 class DatabaseInterface {
 public:
+  DatabaseInterface() = default;
+  DatabaseInterface(const DatabaseInterface&) = delete;
+  DatabaseInterface(DatabaseInterface&&) = delete;
+
   virtual ~DatabaseInterface() = default;
 
+  DatabaseInterface& operator=(const DatabaseInterface&) = delete;
+  DatabaseInterface& operator=(DatabaseInterface&&) = delete;
+
   /**
    * @name Data Reading & Writing
    * @{

cpp/include/loot/game_interface.h

@@ -32,8 +32,15 @@ namespace loot {
 /** @brief The interface provided for accessing game-specific functionality. */
 class GameInterface {
 public:
+  GameInterface() = default;
+  GameInterface(const GameInterface&) = delete;
+  GameInterface(GameInterface&&) = delete;
+
   virtual ~GameInterface() = default;
 
+  GameInterface& operator=(const GameInterface&) = delete;
+  GameInterface& operator=(GameInterface&&) = delete;
+
   /**
    * @brief Get the game's type.
    * @returns The game's type.

cpp/include/loot/plugin_interface.h

@@ -40,8 +40,15 @@ namespace loot {
  */
 class PluginInterface {
 public:
+  PluginInterface() = default;
+  PluginInterface(const PluginInterface&) = delete;
+  PluginInterface(PluginInterface&&) = delete;
+
   virtual ~PluginInterface() = default;
 
+  PluginInterface& operator=(const PluginInterface&) = delete;
+  PluginInterface& operator=(PluginInterface&&) = delete;
+
   /**
    * Get the plugin's filename.
    * @return The plugin filename. If the plugin was ghosted when it was loaded,