Update for Elgg 1.9

I've tested if it works on Elgg 1.9 and made the following changes:

* made some minor changes to get it fully compatible with Elgg 1.9,
* full i18n support,
* restored full functionality (e.g. table layout, display of user icons) and removed obsolete code ("search by domain"),
* cleaned up the code where necessary,
* added German translations.

I hope you like what I've done. It might not a bad idea to upgrade also Bulk-User-Admin version at the community site, if you accept my changes, because there are people asking for the functionionality offered by the plugin once in while (just yesterday - which made me start working on the new version).