project: close #165; Split Database into two modules

- Split _Database_ into _Database_ and _DatabaseSchema_ modules
idgames_db_dump: issue #165; refactor check_schema for idGamesDB
idGamesDB: issue #165; refactored for Database role split
Roles/Database: remove POD for new() method

- Since Database is now a role instead of a first-class object, the
  `new()` method will no longer be used on it; remove the POD that
  says that `new()` could be called
- Added a warning when creating the database using `:memory:` as the
  filename attribute
DBTool: issue #158; more refactoring/cleaning after creating