Fix id in the appdata file

[dagargo]

ID in the appdata file does not follow the specification.

elektroid/res/elektroid.appdata.xml

Line 4 in a8162d5

<id>elektroid.desktop</id>

See https://docs.flathub.org/docs/for-app-authors/metainfo-guidelines/#id and https://www.freedesktop.org/software/appstream/docs/chap-Validation.html#asv-cid-desktopapp-is-not-rdns. This might break things to the point of resubmitting the application to Flathub so this needs to be checked.

Besides, changing the ID would need to change the desktop file but this makes the application icon to not show. Perhaps the icon names need to be changed too.

Finally, it needs to be checked if this ID would break the already existing packages.