Update rails (new patch-level).

See merge request !73

Mitigates a possible XSS vulnerability in ActionView (CVE-2020-5267).

Implement `deliver_selfsent`

Closes #112

See merge request !70

Update rack and nokogiri.

See merge request !71

3.5 is required for deliver_selfsent.

Wording for send_encrypted only.

See merge request !72

Some people misunderstand send_encrypted_only as applicable to all
emails that are being sent, not only to emails to subscribers. This
change in wording could help a little to avoid that.

Upgrade to Rails 5.x

See merge request !66

api uri helper

See merge request !69

with the previous patch it's possible that we don't need it anymore

With this patch we are now using configured api host and port instead of
`localhost`. This allow to use a container/vm for the API without
changing the config for the tests
With the stub_request...to_rack the `allow_localhost` option on WebMock
does not seems used

Fix rendering error message when list.key is not available

See merge request !68

When a key is not found ActiveResource::ResourceNotFound is raised as a
result a 404 is rendered because of `rescue_from` in the
application_controller.
With this patch we are returning nil so we can show the error defined on
_list_menu to the browser.

Relates !68

Relates !68

This comment might contain some changes that should have been included
in the one containing the update to rails 5.1, but unfortunately I can't
debug which those are.

The encrypted secrets feature is not used by schleuder-web, neither is
the built-in support for custom configuration.

I tried to migrate the configuration so that the behaviour of the
application doesn't change through the upgrades to 5.x.

Both ruby versions do not receive any updates anymore, so we may drop
them

Bump rack from 1.6.11 to 1.6.12

See merge request !67

Allow configurable and multiple superadmins.

See merge request !65

fix README.md

See merge request !64

show screenshot

Make codespell happy

See merge request !63