Upgrade Administrate to work with Rails 5

Created by: teoljungberg

This PR upgrades Administrate to work with Rails 5. The changes are backwards compatible to Rails 4.2 which we support.

Changes:

• Set active_record.time_zone_aware_types for Rails 5.

• Replace column_types It was removed in the following commit to rails/rails

• "Sanitize" order parameters to quell warnings.

• Add HTTP method shims This provides backwards compatibility from Rails 5 to 4.

  Inspiration:

  • https://github.com/thoughtbot/clearance/pull/639
  • https://github.com/thoughtbot/high_voltage/pull/229/files

• Configure serving public assets to work with Rails 4 and 5.

• Only set raise_in_transactional_callbacks if < Rails 5. The option is deprecated in Rails 5.

• Upgrade ActionController configuration for Rails 5

• Remove unused spec helper

• Only remove the XML parser if < Rails 5

• Add appraisals for rails 4.2 and 5.0. Add binstub for appraisal.

• Lax Rails version requirement. Lock in 4.2 < Rails::VERSION < 5.1.

• Use fork of administrate-field-image. Which relaxes the version requirement for Rails.

• Upgrade rspec-rails