Modify ApnEditor app for new APN schema.

As the telephony db is changed, The ApnEditor app has to be changed also.
As your request, I changed the ListPreference object to read-only CheckBoxPreference object and "The Others" to "Unspecified".This is a pair set with below change-ids.
- https://partner.source.android.com/g/#/c/8515/
- https://partner.source.android.com/g/#/c/8517/
- https://partner.source.android.com/g/#/c/9048/

Change-Id: I2bdd4f3076adfbee0f277ddb59a150e51e45ac9b
bug:4991683