Core/Scripts: Split the huge scriptloader into smaller pieces

* Each subdirectory contains it's own translation unit now
  which is responsible for loading it's directory
* Improves merging & decoupling between 3.3.5 <-> 6.x
* Removes unused Battleground loader
* Ref #15671

src/server/scripts/Custom/CMakeLists.txt

@@ -1,18 +0,0 @@
-# Copyright (C) 2008-2016 TrinityCore <http://www.trinitycore.org/>
-#
-# This file is free software; as a special exception the author gives
-# unlimited permission to copy and/or distribute it, with or without
-# modifications, as long as this notice is preserved.
-#
-# This program is distributed in the hope that it will be useful, but
-# WITHOUT ANY WARRANTY, to the extent permitted by law; without even the
-# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-
-# file(GLOB_RECURSE sources_Custom Custom/*.cpp Custom/*.h)
-
-set(scripts_STAT_SRCS
-  ${scripts_STAT_SRCS}
-#  ${sources_Custom}
-)
-
-message("  -> Prepared: Custom")

src/server/scripts/Custom/custom_script_loader.cpp

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2008-2016 TrinityCore <http://www.trinitycore.org/>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+// This is where scripts' loading functions should be declared:
+
+
+// The name of this function should match:
+// void Add${NameOfDirectory}Scripts()
+void AddCustomScripts()
+{
+}