Fix display of section end times

The production servers are set to use UTC time, and the app is
configured to know to use the 'America/New_York' timezone.  The issue
was that when calculating the end time for a course based on the start
time + duration, it was using `Time.at (which directly uses the operating
system time) vs. using `Time.zone.at` (which applies the time zone
configured in the application).

Also switched to using `Time.current` rather than `Time.now` (Time.current is
an alias for Time.zone.now).
Updated gem versions

There was a bugfix for simple_calendar gem that fixes the issue with
events displaying on the previous day.  While I was updating that gem I
figured I'd go ahead and update all of them.

These gems were updated (for reference):

- simple_calendar 1.1.8 => 1.1.9
- rake 10.3.2 => 10.4.2
- sprockets-rails 2.2.0 => 2.2.2
- autoprefixer-rails 4.0.0.1 => 4.0.1.1
- code-climate-test-reporter 0.4.1 => 0.4.3
- guard 2.8.2 => 2.10.1
- icalendar 2.2.0 => 2.2.1
- puma 2.9.2 => 2.10.2
- sprockets 2.11.3 => 2.12.3
- redcarpet 3.2.0 => 3.2.1
- sass-rails 4.0.4 => 4.0.5
- spring 1.1.3 => 1.2.0
- listen 2.8.0 => 2.8.3
Merge pull request #3 from cit-jmu/fix_dates_and_times

Fix date/time Issues