catch invalid DIRECTIONS==3 coding in import_highway_projects.py

[tk-oleary]

Add error catching in import_highway_projects.py. e.g.,:

• If DIRECTIONS == 1 or 2, all of the '2' columns (e.g., 'THRULANES2', 'FEET2') should be empty
• If DIRECTIONS == 3, all of the '1' and '2' columns should be filled

(Since "modify" is an option, may work best as a warning message-- not an error.)