added placeholder for notary and arbitrator-tables if they are empty.

If no notaries/arbiters can be found, there is nothing shown. The user does not know what "The addresses below are your trusted arbiters for transactions." is referring to. I added a placeholder "No arbiters found" for that case, so that users know what is going on.

I also changed the indentation/formatting a little bit to better reflect the DOM-hierarchy (IMHO).