R1:1c9a8ccb7c8e

Added Search Box Preferences

Summary:
Resolves T989
- users can now disable the '/' keyboard shortcut which focuses the
search box
- users can now disable the jump nav functionality of the search box

Test Plan:
- verified that the '/' keyboard shortcut works with preference enabled
or unset
- verified that '/' no longer has any effect and disappears from
keyboard shortcuts help overlay with preference disabled
- verified that search boxes have jump nav capabilities with jump nav
functionality…