Add Preference to Disable Auto-Complete

Auto-complete is getting in the way of the very commonly used Return, Arrow Up, Arrow Down keys.

For example, I have 'kids' in vocabulary, and I'm trying to type 'KIDS' as the last word in the line. If I type 'KIDS', the auto-complete shows with 'kids' (lowercased), and if I press Return, it changes it to 'kids'.

Another example, I have 'nicest' in vocabulary, and I want to type 'nice'. That will keep auto-completing to 'nicest' unless I hit the Escape key first.

There's probably a related fix (#178) to auto-complete UX to default to list the closest match first, so if I have 'KIDS' and 'kids' in my vocabulary, when I type 'KIDS', 'KIDS' should be the first option (it is currently not - I'm unsure how it's ranked, by frequency?)

Anyway, this is popping up very frequently in my first hour of use.