Oa_Cite_Identifiers and Google Spreadsheet Import

Perseids support for simple annotations, encoded in OA, stored as items in a CITE collection, and creation of them via import from Google Spreadsheets adhering to predefined templates. 

See PerseusDL/perseids_docs#179

Also encapsulates knowledge of the API agents.yml into a new AgentsHelper class. This comes from the Eagle branch, and pulls a dependency on the mediawiki api client with it. (The mediawiki api client code is a customized version of that gem, downgraded for Rails 2, hence included in vendor/gems)