Memory fixes

1. Locked IceCube gem to 0.11.1 - last version known not to have memory leaks (did not seem to have any effect in our case, but just to be safe)
2. Restricted ApplicationController before_filters to non-xhr requests only (minor optimization) 
3. Refactored blacklisted_url method (lowers max memory usage by 10-70Mb)

*Minor fix:*
1. Added event_instances.js to the precompile list

**Note:**
This config was tested on Puma server with 1 worker at 60 requests/sec - 6 browser tabs on `/hangouts` page, with 60 hangouts - 1 event/2 participants/1 project each - refreshing 10 times per sec.
Max memory usage 450Mb and does not grow further.

Removing new_relic gem - lowers max memory by 0-50Mb.