Incorrect date ranges should provide a human readable error

[mikfreedman]

When you do something silly like try and create a location event that starts today and goes to tomorrow, the start and end of the range are parsed weird (today's date is parsed as next year).

This causes the range to start after it ends and produces a really gross error.

./bin/calendar-assistant location-set Kalamazoo 2/21..2/22
Traceback (most recent call last):
... 
/Users/.../gems/google-api-client-0.28.4/lib/google/apis/core/http_command.rb:228:in `check_status': timeRangeEmpty: The specified time range is empty. (Google::Apis::ClientError)