Refactor setup wizard-related code

Extracted setup-related code from WifiSettings, putting it into a new
derived class, WifiSettingsForSetupWizard.

Set taskAffinity to com.android.wizard, for alignment with other
setup wizard-related tasks.

Change-Id: If371f219dac5d3eff8f7899c16cc6f9475be47cf
7 files changed