Orphan Excel Importer

Part of Jira story: https://osraav.atlassian.net/browse/OSRA-70

Task: https://osraav.atlassian.net/browse/OSRA-163

- Using roo gem to parse Excel files
- Using rails_config gem to read yaml configuration settings for the importer
Need tests for handling invalid options (L74-76), and for when `col.type` is none of the expected types (i.e. `else` on L86)