Feature/asian ngo dataloader

A data loader for Asian NGO collection(from archive.nyu.edu) with spec and cucs. The data loader uses oai client gem :
https://github.com/code4lib/ruby-oai
I also changed the way method catalog_helper#render_external_links handles exceptions
I added files:
resource_sets/﻿faculty_digital_archive_ngo.rb
﻿specs/resource_sets/faculty_digital_archive_ngo_spec.rb
eatures/cassettes/Search_for_NGO_report.yml
and modified files:
Gemfile
features/search.feature
helpers/catalog_helpers.rb
presenters/url_presenter.rb
deploy.rb

@ekate We could keep this function simpler by making a function

```ruby
def oai_client
    @oai_client ||= OAI::Client.new endpoint_url
end
```