Convert datetimes to UTC before storing to db

@maxfliri
RSpec config file

@maxfliri
Restore DST when loading dates from db

@maxfliri
Test converted to rspec one-liner syntax

@maxfliri
Configurable timezone

@maxfliri
DateTime property now handles nils

@maxfliri
Change version to 0.4.0

 Changes:
 - DateTime's always stored in the equivalent UTC time
 - DateTime's loaded with a configurable timezone, adding DST offset when
   appropriate

@maxfliri
Reset default timezone before each test

@robyoung
@maxfliri
Handle nils when dumping to db

  Also, add integration tests for datetime proeprties

@maxfliri
Check query conditions are also converted to UTC

@robyoung
@maxfliri
Raise log level to error for tests

@robyoung
@maxfliri
Merge pull request #2 from alphagov/store_utc_datetime

Store UTC datetime