Clean up custom cell layout style for Months screen...

Split the logic for drawing each border into
cumulative sections, starting from conditionals
requiring the fewest measures to those requiring
the most.
Fix custom cell layout style for Months screen...

The top border doesn't draw for cells on a full
last row, due to the isOnPartialLastRow test
failing by not accommodating if the last row is
actually a partial last row. Add the
hasPartialLastRow test to solve.