improve login

[VladimirAlexiev]

1. The home page says:

To add your Linked Data solution to the graph,
... request([9]) an account to the Publications Office of EU.

I think this is incorrect. It should say:

... you can use your EU Participation Portal account. If you don't have one, click Register on that page. Then use the EU Login link on the top right of this site and confirm to EU Webgate.

2. I think you should honor Wikipedia/Wikidata accounts (also through OAuth). Many potential contributors may not have an EU login but will have a WD login.