Make event-indicator a link to the events page, with new events highlighted

Currently it works as a reload button, but it gives you nothing but dismissing the indicator unless you are on the events page, and in any case you have no idea which events are newly created.

With this change, clicking the indicator takes you to the events page on which newly created events are highlighted.

![indicator](https://cloud.githubusercontent.com/assets/10236/4660694/cfa384f8-551a-11e4-8c00-04bbba038b55.png)

![events](https://cloud.githubusercontent.com/assets/10236/4660698/d659ae6c-551a-11e4-977d-3bc7ca07568a.png)

Personally, I think something like this will be clearer to the next person if we can avoid lambdas:

```ruby
def highlighted?(id)
  @event_highlight_ranges ||= (params[:highlight] || '').split(/,/).flat_map do |part|
    case part
    when /\A(\d+)\z/
      (part.to_i)..(part.to_i)
    when /\A(\d+)?-(\d+)?\z/
      infinity = (1/0.0)
      ($1 ? $1.to_i : 1)..($2 ? $2.to_i : infinity)
    else
      []
    end
  end

  event_highlight_ranges.any? { |range| range.cover?(id) }
end
```