Add .ruby-version to git ignore
[GEM] Update elasticsearch libraries

* Remove re-Tire
* Add elasticsearch-model
* Add elasticsearch-rails
Remove index_all script
Include elasticsearch instrumentation module
Initialize kaminary hooks for elasticsearch
Add elasticsearch rake tasks
Remove unused method delete_index from spec_helper
Adapt Issue model to the new elasticsearch library
Adapt User model the new elasticsearch library
Create elasticsearch test indexes when running the specs
Remove regression for Ruby version
Test against Ruby 2.1.X