Per-service email preferences

Closes #80 (closed)

Also fixes a minor bug introduced by 4bc7ffd0 and bad/wrong UI texts and translations.

Service email preferences except for the first one are collapsed if there are more than two settings to keep the selfservice page clean. Clicking on "Show more settings ..." expands the hidden selects and then disappears (i.e. it is not possible to re-collapse the selects).