Adding owncloud.beta: Beta (bleeding edge) version of android owncloud app

Adding beta version of ownloud android app with latest features.

I have written a metadata following https://gitlab.com/fdroid/fdroiddata/blob/master/CONTRIBUTING.md. Now I should try "fdroid build -v -l app.id" with my app.id. But it fails with "fdroidserver.common.FDroidException: No apps to process." All previous commands ran successfully. So I could not build the app.