Remove User#at_midnight

Replace it with a class called DateUtils with a method called
`#midnight_for` that takes a preference instance and date to convert to
midnight.
clean up whitespace
Fix a date-based issue in the project tests

Due to time zone issues, this test was failing for me because it was
attempting to compare a date in my local time zone with a UTC date.
rename DateUtils to UserTime
Replace User#time with UserTime#time
Merge pull request #202 from TracksApp/extract-extras-from-user

Extract time and date concerns from User