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
What do you think about extracting the `last_row` validation into a separate method and using it with `return`: 
```ruby
return unless file_contains_records?
CONFIG.first_row.upto...
```