Allowing Will/Ben the possibility to hack the date but not confuse PST

We found out the server were using GMT , which means that the challenge will close early for all American users.

We can hack the date but then it would look like the challenge is closing a day later and again lead to confusion.

SO - as a short-term hack I've provided a waffle switch (use_hacked_PST) that will subtract 8 hours from the current end_date. This means we can set the challenge end_date to be April 6th, 07:59 GMT but have it display as closing at April 5th 11:59 - which is what the PST users would be expecting.