Huge refactoring on Mappers architecture and organization

Added concept of Open mapper which replaces BaseMapper and EmptyMapper
ModelMapper extends OpenMapper and mirrored as Mapper for compatability

Other accompanying updates

Task 13165
Bump version
Delete flat_map/mapper.rb acidentally left from previous version

Task 13165
Merge TMXCredit/flat_map#3 v0.1.0 'origin/13165_open_mapper_approach'

Task 13165
Task 13299

* origin/13165_open_mapper_approach:
  Delete flat_map/mapper.rb acidentally left from previous version
  Bump version
  Huge refactoring on Mappers architecture and organization