added support for Model migrations

now we have a table core.migration and each model (User, Group, Item, ItemContent and a new Migration) have its own
row in the table with a version number

added to config:
db_make_migration_if_needed and db_stop_if_migration_fails (need description yet)

winixd/db/db.h

@@ -61,7 +61,7 @@ public:
 		is_postgresql_smaller_than_10 = false;
 	}
 
-	void PostgreSQLsmallerThan10(bool is_smaller_than_10);
+	//void PostgreSQLsmallerThan10(bool is_smaller_than_10);
 
 	/*
 	bool  GetUserPass(const std::wstring & login, long & user_id, UserPass & up);