Make the built-in search enabled by default.

Rationale: The built-in search is easier to use for new users and does not rely on the browser integration (which uses a lot of trouble for users and needs quite some technical explaining if it does not work as expected). Also the "Lookup in browser" functionality is still available separately, even from within the search dialogs.

We keep the option. The browser based search can offer more flexibility, as it allows using all the search functionality the MB website has to offer. Hence advanced users might want to turn off the built-in search.