Added gems:
- therubyracer
- activerecord-import
- debugger
- hirb
- shoulda-matchers
- timecop
Added shoulda/matchers to spec_helper.rb
In Exchange:
1) Required open-uri
2) Added currencies association
3) Added name validations
4) Added before validation callback
5) Added bodies of get_nbp_xml and save_current_rates methods
6) Added xml_list and xml_name methods