Fix deprecated top-level developer_name in AppData XML

[musicinmybrain]

Use the name element in a developer block instead, as recommended by appstreamcli 1.0.0.

This fixes all warnings when validating the AppData XML file, although there are still informational messages:

I: io.github.lainsce.Notejot:37: description-first-para-too-short
     A stupidly-simple notes application for any type of short term notes or ideas.
   The first `description/p` paragraph of this component might be too short (< 80 characters).
   Please consider starting with a longer paragraph to improve how the description looks like in
   software centers and to provide more detailed information on this component immediately in the
   first paragraph.

I: io.github.lainsce.Notejot:91: nonstandard-gnome-extension kudos
   This tag is a GNOME-specific extension to AppStream and not part of the official specification.
   Do not expect it to work in all implementations and in all software centers.

I: io.github.lainsce.Notejot:95: developer-id-missing
   The `developer` element is missing an `id` property, containing a unique string ID for the
   developer. Consider adding a unique ID.

✔ Validation was successful: infos: 3, pedantic: 2

[musicinmybrain]

Let me clarify that appstream 1.0.0 has not yet been released, and my appstream is a pre-release as currently packaged in Fedora Linux Rawhide (the development version of the OS), corresponding to https://github.com/ximion/appstream/commit/d88ed03cb5b3b1803bdee3528c9b99d528ceb065. See also https://github.com/ximion/appstream/issues/244.

[musicinmybrain]

As of appstream 1.0.2, the deprecated developer_name tag has been downgraded to info (I think this happened in 1.0.1), but in this PR, appstreamcli validate has started warning (and exiting with nonzero status) about the lack of an id property on the developer element:

W: io.github.lainsce.Notejot:95: developer-id-missing
   The `developer` element is missing an `id` property, containing a unique string ID for the
   developer. Consider adding a unique ID.

Per https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-developer, “The element should have a id property, containing a unique ID to identify the component developer / development team. It is recommended to use a reverse-DNS name, like org.gnome or io.github.ximion, or a Fediverse handle (like @[email protected]) as ID to achieve a higher chance of uniqueness.”

I’m modifying this PR to propose using us.lainsce as the developer ID.