* Fix boolean columns sometimes having a null value

* Fix wrong value being set instead of null

* add annotate to Gemfile

* rails g annotate:install

* configure annotate_models

* add schema info to models

* fix rubocop to add frozen_string_literal

```
*An* `ActiveRecord::StatementInvalid` *occurred while* `POST </settings/import>` *was processed by* `imports#create`
Exception
----------------
PG::NotNullViolation: ERROR:  null value in column "type" violates not-null constraint
```

* Allow export of mutes list

* Allow importing of mutes list

* Refactor to use Settings::Exports::BaseController and DRY up exports code