Admin reports with accounts (#2092)

* Add a ReportFilter class

* Add reports and targeted_reports relationships to Account

* Use ReportFilter from admin/reports controller

* Link to admin/reports filtered views from admin account show view

* Add indexes to reports.account_id and reports.target_account_id

db/migrate/20170418160728_add_indexes_to_reports_for_accounts.rb

@@ -0,0 +1,6 @@
+class AddIndexesToReportsForAccounts < ActiveRecord::Migration[5.0]
+  def change
+    add_index :reports, :account_id
+    add_index :reports, :target_account_id
+  end
+end