Update for Elgg 1.9, code cleanup and German translations added

Here's the PR that I've mentioned in issue #2. The plugin will work now on Elgg 1.9 (for the direct download to work again the Elgg community site needs to get updated first to give the correct download url - PR for this issue already made). I've also tried to clean up the code a little bit and additionally added German translations. The Danish language file is missing some strings though at the moment which I was unable to provide.