Let git track modules subdirectory

For this project we're going to try to keep custom, not-very-reusable
modules and features in the installation profile repo.  This might
not be a good idea.
Add content types

Add Person, Board and Board Term content types to reflect the
application business models.

Board Term uses entity_reference fields to create a many-to-many
relationship between a Person and a Board.  Eventually, we'll add
a date field to designate the duration of a particular term.
Add "Term Dates" field to Board Term content type

This is a single Date field, with both a start and end date to
designate when a particular board member's term starts and ends.