ModelView for get_gantt_data #1955

* This patch includes the __register__ method in a view model
  'TimesheetEmployeeDay' to create a relation for running get_gantt_data
  and get_comparison_data

Issue ID: 242002
Task ID: project-7/task-1955
Merge pull request #23 from simmianand/feature/task-1955

[my_openlabs] ModelView for get_gantt_data #1955