Ensure overlaps_with_timerange and intersect_with are consistent

[philipnbbc]

Details

It makes sense to view an overlap occurring if the intersection is not empty.

The same should also happen to the special case of never() and eternity() timeranges. It should return False given that intersect_with returns an empty (never()) timerange.

This also resulted in fixes to the tests for is_contiguous_with_timerange where a timerange is never().

Pivotal Story

Story URL: https://www.pivotaltracker.com/story/show/188190520

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