Add Core.DisplayCalendarEvents

Sample that shows how to use REST API to retrieve calendar events and process them in order to display them using a third party component which has features SharePoint does not such as tooltip information on when hovering over an event, or multiple calendar overlays with custom styling based on event properties, etc...  Encapsulates all the logic specific to sharepoint events into file: SP.Calendar.js which other people could use in their projects to achieve similar results using their preferred framework.