Added creation of ChirpTask Calendar

This commit allows ChirpTask to create and maintain a Google Calendar
by its Calendar ID if there isn’t one that was created by ChirpTask
before.

If there is already a ChirpTask calendar, it would be used as the main
calendar to work on.

By making the above possible, CalendarHandler class is created to
provide static methods for CalendarController to call to make actions
related to Google Calendar service.

ChirpTask will store the Calendar ID in its newly created file
“credentials/googlecalendar/ChirpTaskTimedTaskCalendarID.txt”
Updated gitignore to ignore googlecalendar folder

Gitignore is updated to ignore the entire /credentials/googlecalendar/
folder. This folder will contain user-specific files such as the file
that stores the Google Calendar ID that ChirpTask maintains.
Renamed variables in TasksHandler class

Removed the “_” prefix where applicable to the variable names in the
TaskHandler class.