Break this repo up into core functions and personal stuff

[macdonaldster]

This repo is a mishmash of util functions like the code to fetch column headers, core functionality like the auto-advancement of TODOs as calendar entries, and my own personal utilities like the code that adds a habit to my calendar every day at 2:30pm. This should broken up into three files:

1. Core.gs
2. TodoManagment.gs
3. PersonalHacks.gs

PersonalHacks.gs would basically be my own code but people could use it as-is or modify it (either in a fork or by making a copy of it in their own sheet, etc).