Explicitly show action bar in test prior to hiding.

This test was still passing even if `SettingsFragment#onStart()` was removed because the action bar is hidden by default in the test harness.
Tests existing preferences in SettingsFragment.
Adds zoom prefs.
Displays current value as summary.
Replace dash character in strings.xml to fix lint errors.
Merge pull request #150 from mapzen/chuck/zoom-prefs

Adds zoom preferences