Memory fixes

1. Locked IceCube gem to 0.11.1 - last version known not to have memory leaks
2. Restricted ApplicationController before_filters to non-xhr requests only

Minor fix:
1. Added event_instances.js to the precompile list

Note:
This config was tested on Puma server with 1 worker at 20 requests/sec - max memory usage 460Mb.
Removing new_relic gem - lowers max memory usage to 430 Mb.  New relic can be used wittout a gem, by configuring new_relic addon in Heroku dashboard.