Code style fixes

Sorry for the completely generic title here. This makes one functional change, and a couple of code style changes to settings.js

- the notifications checkbox was only enabled if `webkitNotifications` was on window. Chrome has removed this (and Firefox its equivalent too), so the correct condition should include these. I didn't remove the check on the `webkitNotifications` property, since I don't know how much old browser support you want to keep. It's been a while since it was removed anyway, so I think it could go.

Code style changes:
- The use of `this.$('...')` vs `$('...', this.$el)` was inconsistent. I changed to use the former since it's shorter and a standard backbone method
- There was a lot of repeated code in the translations that was shortened with a small helper function
- Typo in one of the method names.