appdata: Add developer ID

Flathub requires a developer tag and developer ID. Also Appstream decided to use rdns structure for developer ID.

It allows reverse-dns IDs like sh.cozy, de.geigi or Fediverse handle (like @user@example.org)

> A developer tag with a name child tag must be present.
> Only one developer tag is allowed and the name tag also must be present only once in untranslated form.

```
<developer id="tld.vendor">
  <name>Developer name</name>
</developer>
```
Source: https://docs.flathub.org/docs/for-app-authors/metainfo-guidelines/#name-summary-and-developer-name

> 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.

Source: https://www.freedesktop.org/software/appstream/docs/chap-Metadata.html#tag-developer

data/me.iepure.Ticketbooth.metainfo.xml.in

@@ -14,6 +14,9 @@ SPDX-License-Identifier: CC0-1.0
 	<launchable type="desktop-id">@[email protected]</launchable>
 	<summary>Keep track of your favorite shows</summary>
 	<developer_name translate="no">Alessandro Iepure</developer_name>
+	<developer id="me.iepure">
+		<name translate="no">Alessandro Iepure</name>
+	</developer>
 	<description>
 		<p>Ticket Booth allows you to build your watchlist of movies and TV Shows, keep track of
 			watched titles, and find information abme.iepureout the latest releases.</p>