moved session to namespace query and move basic_schema::initialize to session constructor

source/orm/CMakeLists.txt

@@ -1,6 +1,5 @@
 add_library(matador-orm STATIC
-  ../../include/matador/orm/error_code.hpp
-  ../../include/matador/orm/session.hpp
+  ../../include/matador/query/session.hpp
   ../../include/matador/query/abstract_pk_generator.hpp
   ../../include/matador/query/attribute_string_writer.hpp
   ../../include/matador/query/basic_schema.hpp
@@ -120,8 +119,7 @@ add_library(matador-orm STATIC
   ../../include/matador/sql/sql_functions.hpp
   ../../include/matador/sql/statement.hpp
   ../../include/matador/sql/statement_cache.hpp
-  orm/error_code.cpp
-  orm/session.cpp
+  query/session.cpp
   query/abstract_pk_generator.cpp
   query/attribute_string_writer.cpp
   query/basic_schema.cpp