added grouping to instance configuration UI

based on namespace prefixes - now each group has its own FIELDSET, which
makes it less chaotic

note that there's no explicit order yet - due to Ruby 1.9 hashes
retaining order and because the existing translations (DE and EN) just
happen to provide the right alphabetical order ("common", "languages",
"triplestore") - this should be easy to change later (patches welcome!)