Configurable units fixes

Configurable units fixes

Notable changes:
- Add pressure unit to the units model.
- Add tire pressure unit configuration page under settings.
- Rework the VSS client, provider, and the associated handling in
  the vehicle and audio state providers to make the signal updating
  code reusable for processing the result of VAL API get commands.
- Add logic to get the initial values of the used VSS signals so
  the initial application state looks sane in demo scenarios.
- Add VSS signal support to the units provider so that changes will
  be pushed out for e.g. IC use.
- Fix pressure unit use in various widgets.
- Fix up range calculation for dashboard to correctly account for
  units and the incoming VSS value being in meters.
- Fix some unit naming inconsistencies around capitalization.

Bug-AGL: SPEC-5031, SPEC-5032

Change-Id: I33ac735dfbe35283bd30c92aa157cbdb7af1837c
Signed-off-by: Scott Murray <scott.murray@konsulko.com>