[NewAdmin BO] Add routes to namespace and countries/elections resources
[NewAdmin BO] Admin backoffice dependency in Gemfile

*  Bootstrap
*  Bootstrap Datepicker
*  Simple Form
*  Select 2
[NewAdmin BO] to_s functions to models country and election
[NewAdmin BO] Stylesheet and javascripts assets to new_admin backoffice
[NewAdmin BO] new_admin backoffice controllers for countries and elections
[NewAdmin BO] Base layout
[NewAdmin BO] Views for countries and elections
[NewAdmin BO] Use country_id instead of country in election form
[NewAdmin BO] Use cancan load_resource to simplify code
[NewAdmin BO] Fix update election path
[NewAdmin BO] destroy action on election
[NewAdmin BO] Configuration of simple form to use it with bootstrap
[NewAdmin BO] icons in election form
[NewAdmin BO] Country column in election index
[NewAdmin BO] Tags resources in rouing file
[NewAdmin BO] Add Tags in layout navbar
[NewAdmin BO] Add basic tag management and search
[NewAdmin BO] Remove separate tags management
Gem : pry-rails to development group
Gem : Underscore to add some JS utility functions