@laurabrown => Get a system time offset from the Artsy servers

For people following along at home, I will inline describe what is going on. 

At an auction we want to ensure that timezones do not become an issue, for example if the artsy servers are on a different time zone to the auction we want to ensure all dates are kept sanely in sync. 

So there's an Artsy time service. I've made a `SystemTime` object that we can use to get the correct date from whenever a date is needed. It knows if it's in sync, if it isn't it returns today's date. This is basically a direct swift port of what we use in Eigen ( the iPhone app ).

@AshFurrow can you give it a one-over too.
We decided at the start of this project that these parts of the template were basically useless. All of this data is available in the git history, and more up to date. It's common on obj-c projects, but again, useless.