Web 2324 calculare arrival dates

* Added moment-timezone module. 

* Added some basic function level documentation - good thing to start applying? Used the JSDoc format as defined here: https://google-styleguide.googlecode.com/svn/trunk/javascriptguide.xml#Comments

* Logic for calculating arrival time using timezones, departure date/time and flight duration. I've added some test cases for basic timezone scenarios and on edge case with BST. Didn't want to add too many tests since it would be testing the logic of another lib (moment-timezone) but wanted enough to test that the calculateArrival function worked in concept.

* Refactored structure of unit tests to bring into line with other repos (all.js/util.js).

* Updated existing logic/tests re: how are are constructing new moment instances based on this: https://github.com/moment/moment/issues/1407