Upgrade to latest Rails 4.2.x release

[schultyy]

In order to upgrade the application to the latest 4.2.x release, the following things need to be taken into consideration:

Rails 4.1:

• use secrets.yml
• CSRF protection from remote <script> tags

Rails 4.2:

• add responders gem to keep respond_to functionality
• Check *_filter methods, they've been renamed to *_action

These points above are not complete. I browsed through http://guides.rubyonrails.org/4_1_release_notes.html and http://guides.rubyonrails.org/4_2_release_notes.html#upgrading-to-rails-4-2 and checked if points listed do concern us.

[schultyy]

For more details we also need to consult http://guides.rubyonrails.org/upgrading_ruby_on_rails.html

[schultyy]

For Rails 4.2 we need to update some Gems. bundle update rails with Rails 4.2 in the Gemfile produces this:

[0] % bundle update rails
Fetching gem metadata from https://rubygems.org/
Fetching version metadata from https://rubygems.org/
Fetching dependency metadata from https://rubygems.org/
Resolving dependencies....................................................
Bundler could not find compatible versions for gem "actionpack":
  In Gemfile:
    actionpack-page_caching (>= 1.0.2, ~> 1.0) was resolved to 1.0.2, which depends on
      actionpack (< 5, >= 4.0.0)

    formtastic was resolved to 3.1.3, which depends on
      actionpack (>= 3.2.13)

    inherited_resources (~> 1.6.0) was resolved to 1.6.0, which depends on
      actionpack (< 5, >= 3.2)

    inherited_resources (~> 1.6.0) was resolved to 1.6.0, which depends on
      actionpack (< 5, >= 3.2)

    kaminari (~> 0.14) was resolved to 0.16.3, which depends on
      actionpack (>= 3.0.0)

    rails (~> 4.2.0) was resolved to 4.2.0, which depends on
      actionpack (= 4.2.0)

    rails (~> 4.2.0) was resolved to 4.2.0, which depends on
      actionpack (= 4.2.0)

    activeadmin (~> 1.0.0.pre2) was resolved to 1.0.0.pre2, which depends on
      ransack (~> 1.3) was resolved to 1.7.0, which depends on
        actionpack (>= 3.0)

    routing-filter was resolved to 0.4.0.1, which depends on
      actionpack (< 4.2)

    rspec-rails (~> 3.4) was resolved to 3.4.2, which depends on
      actionpack (< 4.3, >= 3.0)

    simple_form was resolved to 3.2.1, which depends on
      actionpack (< 5.1, > 4)