Update descriptions for onboarding

That's the ticket we should look at for the final strings for the onboarding in case there are changes we need.

Looking over the english ones I only found two things we should change, both on the onion services onboarding pane:

1. s/Browser/browser. Or we could use "Tor Browser" instead of "our Browser".
2. I am quite hesiatant to use "ultimate" because that's a thing I feel we hardly can reach in a security/privacy context and should not claim we'Ve reached. Could we please use something else? Maybe "enhanced"?