Clc 3594 name error in activities feed

https://jira.ets.berkeley.edu/jira/browse/CLC-3594

As Chris pointed out, this was happening because app/models/my_activities/canvas.rb had the same name as Canvas the module.

1. Renamed app/models/my_activities/canvas.rb to app/models/my_activities/canvas_activities.rb

2. Separated the class Canvas from the module MyActivities and renamed the class CanvasActvities to avoid confusion with the modlule already named canvas.

3. Confirmed that the NameError in MyActivitiesController#get_feed no longer appears.