Fix #6893
Fix #9268

* Show exact number of followers/statuses on export page/in tooltip

* Fix tests

* Refactor Export to take an account and know about the export types

* Use Export instance in settings/exports#show

* 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