Completer scrolling

See merge request !20

- Add scrolling
- Only display ~7 items at once

Not only should this prevent hickups, it also fixes a potential crash.

Make nheko usable without a secret storage service

Apply selective clang-tidy suggestions

Currently translated at 100.0% (627 of 627 strings)

Co-authored-by: Linerly <linerly@protonmail.com>
Translate-URL: https://weblate.nheko.im/projects/nheko/nheko-master/id/
Translation: Nheko/nheko

Request inline images in the right size and anti-alias them

- If an inline image has specified a height, add parameters to the
  image:// URI.
- Add scaled to the parameters, the images would be cropped otherwise.
- Extract the height from image:// URI and use it for requestSize.
- Use scaledToHeight instead of scaled.

This change adds the ability to run Nheko without a secrets storage
service[1]. The secrets are stored in plaintext under the [secrets]
section of nheko.conf. Since this is a "I know what I'm doing" type
of feature, it's disabled by default and can only be enabled with an
hidden setting `run_without_secure_secrets_service=true`.

Fixes issue #705.

[1]: https://freedesktop.org/wiki/Specifications/secret-storage-spec

This adds a man page which lists command line options, key bindings and
commands. A new CMake option `MAN` is added, enabled by default on
`UNIX` but not `APPLE`.

The man pages are generated with either `a2x` (from asciidoc) or
`asciidoctor`. If both are not found, a fatal error is signaled.