CYB-226 Engagement Index should be frequently, automatically, updated

* renaming the old Canvas::ApiRequest service to simply "ApiRequest" service, and clean up of its code.
* using new 'keyword arguments' of Ruby 1.9-2.0+ in place of Hash arguments (Ruby 1.8- style).
* Does not complete ticket; done in two PRs to keep the code changes understandable.

A part of 
[CYB-226 Engagement Index should be frequently, automatically, updated](https://jira.ets.berkeley.edu/jira/browse/CYB-226)