Added time zone support to events

I noticed a bug when looking at my list of proposals for RubyConf Australia.

On the initial list it showed the CFP as open:
![screenshot 2014-10-19 23 05 03](https://cloud.githubusercontent.com/assets/10128/4694740/da0ade1c-57d3-11e4-9403-a98e77124f73.png)

However it was actually closed once I clicked through to the show action:
![screenshot 2014-10-19 23 07 07](https://cloud.githubusercontent.com/assets/10128/4694741/e90f5582-57d3-11e4-9dbc-3a6c6caaf581.png)

This is because the conference is in the Australian time zone and I'm in CEST which is still, currently, Sunday before midnight which is when the CFP closes.

I believe that this patch would fix the issue, though haven't tested it.  It's late, and I just wanted to get the patch discussion open.
Why not `Time.current`?