Better search

Finally! :) 
This will solve issues #256 and #274 

Added:
- endless pagination on scroll (using Twitter like endless-pagination)
- ajax search on form control change - no need to press enter anymore (unless you're typing in a keyword)

Removed:
- GET parameter for past events and country as they're picked up from form data
- 3 old files that are not used (search-events.js, pjax_index.html, pjax_search_events.html)

In order for pagination to work with faceted search, I added custom endless pagination js file - I just copied original endless_pagination.js, changed all GET requests to POST requests and pass form data. 
IMHO this was the only sensible option in our case (my opinion based on <a href="http://stackoverflow.com/questions/2266554/paginating-the-results-of-a-django-forms-post-request">this stackoverflow answer</a>). 
@ercchy what do you think? I played around with sessions, but it was causing too many serialization issues. I don't have enough experience with overriding methods from other libraries :)

So... @ercchy can you please take a look at the changes before we deploy?