Appdata related patches

appdata: Remove donation URL

There is a warning about this URL

url-not-reachable: https://liberapay.com/bielmoussaoui - Unexpected status code: 410

appdata: Update appdata

Add categories and keywords support

appdata: Fix description errors

Release entries should be in a description entry.

More information: https://www.freedesktop.org/software/appstream/docs/sect-Metadata-Releases.html

appdata: Mark developer_name as untranslatable

There is no need for translating the developer names.

appdata: Remove purism tags

Duplicated 'Purism::form_factor' entries are preventing the validation of the appdata.

appdata: Use appstreamcli for appdata validation

appstream-util is obsoleted by appstreamcli.