adds the SetFreeTimeViewController

For adding free times in the setview
- to add a start time
- to add an end time
- to save the time interval
- to refresh the set free times table after saving the time interval
adds functionality to send free times to Parse backend

- get the current user
- create a new TimeInterval PFObject, add values to its attributes
- save the timeInteval in background
adds functionality to fetch free times from Parse in the MeetTimeViewController

- query for current users time intervals
- load them into an array
- display times in the table view controller
- reload table every time the tab is clicked