Allow opening .pot files from file manager

For projects that have not previously been translated to the target language,
l10n.kde.org provides download links for the .pot templates.

To make getting started with translation of such projects easier for beginners,
allow Lokalize to be invoked directly on .pot files from file managers.

src/org.kde.lokalize.desktop

@@ -62,7 +62,7 @@ Exec=lokalize %F
 Icon=lokalize
 Type=Application
 Categories=Qt;KDE;Development;Office;Translation;
-MimeType=application/x-xliff;text/x-gettext-translation;application/x-lokalize-project;
+MimeType=application/x-xliff;text/x-gettext-translation;text/x-gettext-translation-template;application/x-lokalize-project;
 X-DocPath=lokalize/index.html
 X-DBUS-StartupType=Multi
 X-DBUS-ServiceName=org.kde.lokalize