AppData additions required for the software center

Hi again!

First, apologies for the direct email. I'm emailing you directly as you've been listed as the 
update contact in one or more AppData files.

We've been busy building an awesome software center, and we've been adding more and more metadata 
fields that upstream authors can set. The software center is now being used in Fedora, Opensuse, 
Ubuntu, Debian and Arch, with many millions of happy users.

Some of the newest features include a way to make it easy for translators to contribute new 
translations of your applications by specifying a URL in the libreoffice-draw.appdata.xml 
libreoffice-base.appdata.xml libreoffice-writer.appdata.xml libreoffice-impress.appdata.xml 
libreoffice-calc.appdata.xml AppData file that tells them where to start looking. This can be 
specified by adding:

<url type="translate">http://the-web-site-with-translation-instructions/</url>

Another useful tag to add is to tell end-users where to donate, for instance:

<url type="donation">http://www.gnome.org/friends/</url>

If it's been some time since you updated the AppData file (and hey, you've got an app to write!) 
you can get add the latest metadata fields by doing `appstream-util upgrade 
libreoffice-draw.appdata.xml libreoffice-base.appdata.xml libreoffice-writer.appdata.xml 
libreoffice-impress.appdata.xml libreoffice-calc.appdata.xml` and then replacing any FIXMEs in the 
file with actual data. We'll be putting more functionality into the software center in the future 
that uses this extra data, but we need more upstream software to opt-in before we can enable 
features, for instance, providing a button for users to donate to specific apps.

You can also use `appstream-util validate-relax` on your AppData file to check the various fields 
meet our style guidelines. If you disagree with any of the validation warnings, please let me know!

Of course, you don't have to do a release with these enhancements straight away, and if you have a 
stable branch it would be a good thing to backport this as well if it does not add translated 
strings or you have no string freeze policy.

When you've changed the file(s) and committed, please email me back and I'll mark your application 
as completed. If you don't want to hear from me ever again just edit the <update_contact> in the 
AppData file and change it to somebody else. I'm not planning on emailing more than once every 6 
months, so don't worry about me spamming you with even more work to do.

Thanks,

Richard