SUW: use standard navigation method

Use software/hardware back button and add on-screen Next & Skip buttons.

Change-Id: I7bfa052f2217e51ea778df688e7169657aaad2c6

src/org/lineageos/setupwizard/WelcomeActivity.java

@@ -35,8 +35,7 @@ public class WelcomeActivity extends BaseSetupWizardActivity {
         super.onCreate(savedInstanceState);
         mRootView = findViewById(R.id.setup_wizard_layout);
         setNextText(R.string.next);
-        setBackText(R.string.emergency_call);
-        setBackDrawable(null);
+        setSkipText(R.string.emergency_call);
         mEnableAccessibilityController =
                 EnableAccessibilityController.getInstance(getApplicationContext());
         mRootView.setOnTouchListener((v, event) ->
@@ -47,6 +46,11 @@ public class WelcomeActivity extends BaseSetupWizardActivity {
     @Override
     public void onBackPressed() {}
 
+    @Override
+    public void onSkip() {
+        startEmergencyDialer();
+    }
+
     @Override
     public void onNavigateBack() {
         startEmergencyDialer();