Added support to display events from all countries

Added two new entries to search form.
Just a quick question: 
Wouldn't  ```if country_filter is not None``` be same as ``` if country_filter``` ? Is there a reasone for ```not None``` part? Furthermore do you at all need to check it's existance, since ```Event.CUSTOM_COUNTRY_ENTRIES``` DOES NOT HOLD ```None``` at all?
So would this ``` if country_filter not in [ custom_country[0] for custom_country in Event.CUSTOM_COUNTRY_ENTRIES ]:``` sufice?