Added some more interaction helpers

Re #95 

Adds count helpers. Had to fix capybara webkit to an older version but seems to work fine.

Allows you now to do things like:

```ruby
@event.confirmed_attendees_count #=> counts number of current interactions on relation 'attendees' with type 'confirmed'
@event.confirmed_and_attending_attendees_count #=> same as above but counts 2 types
@event.confirmed_and_not_attending_attendees_count #=> allows for mixing in "not"
@event.all_attendees_counts #=> returns a hash with all current counts
```