Refactor exports controller (#1567)

* Add basic coverage for settings/exports controller

* Remove unused @account variable from settings/exports controller

* Add coverage for download export actions

* Remove deprecated `render :text` in favor of `send_data` for csv downloads

* Add model to handle exports

* Use Export class in settings/exports controller

* Simplify settings/exports controller methods

* Move settings/export to more restful routes

spec/models/export_spec.rb

@@ -0,0 +1,17 @@
+require 'rails_helper'
+
+describe Export do
+  describe 'to_csv' do
+    it 'returns a csv of the accounts' do
+      one = Account.new(username: 'one', domain: 'local.host')
+      two = Account.new(username: 'two', domain: 'local.host')
+      accounts = [one, two]
+
+      export = Export.new(accounts).to_csv
+      results = export.strip.split
+
+      expect(results.size).to eq 2
+      expect(results.first).to eq 'one@local.host'
+    end
+  end
+end