[GEM] Update elasticsearch libraries

* Remove re-Tire
* Add elasticsearch-model
* Add elasticsearch-rails
Remove index_all script
Include elasticsearch instrumentation module
Initialize kaminari 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
Add elasticsearch_client initializer
Introduce searchable module
Change index action in issues api controller
Add a very naive search action for issues
Introduce ElasticsearchQuerySanitizer
Autoload lib directory when booting the application
Move ES logic from user model to the Searchable::User module
Breaking spec wip
Merge pull request #21 from Jarviis/elasticsearch/lib_update

Elasticsearch/lib update