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: net.sourceforge.qtpfsgui.LuminanceHDR:20: screenshot-media-url-not-secure
     http://qtpfsgui.sourceforge.net/screenshots/MainWindow.png
   Consider using a secure (HTTPS) URL to reference this screenshot image or video.

I: net.sourceforge.qtpfsgui.LuminanceHDR:24: screenshot-media-url-not-secure
     http://qtpfsgui.sourceforge.net/screenshots/Tonemapped-image.png
   Consider using a secure (HTTPS) URL to reference this screenshot image or video.

I: net.sourceforge.qtpfsgui.LuminanceHDR:28: screenshot-media-url-not-secure
     http://qtpfsgui.sourceforge.net/screenshots/HDR-Wizard-1st-page.png
   Consider using a secure (HTTPS) URL to reference this screenshot image or video.

I: net.sourceforge.qtpfsgui.LuminanceHDR:32: screenshot-media-url-not-secure
     http://qtpfsgui.sourceforge.net/screenshots/Batch-TM.png
   Consider using a secure (HTTPS) URL to reference this screenshot image or video.

I: net.sourceforge.qtpfsgui.LuminanceHDR:42: developer-id-missing
   The `developer` element is missing an `id` property, containing a unique string ID for the
   developer. Consider adding a unique ID.

I: net.sourceforge.qtpfsgui.LuminanceHDR:46: url-not-secure http://qtpfsgui.sourceforge.net/
   Consider using a secure (HTTPS) URL for this web link.

✔ Validation was successful: infos: 6, pedantic: 1

[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 ximion/appstream@d88ed03. See also ximion/appstream#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: net.sourceforge.qtpfsgui.LuminanceHDR:42: 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 @user@example.org) as ID to achieve a higher chance of uniqueness.”

I’m modifying this PR to propose using net.sourceforge.qtpfsgui as the developer ID.