Add SipAddress to ContactsContract.

This is a new data kind representing a SIP address for a contact.
The new class is ContactsContract.CommonDataKinds.SipAddress,
and the new mime type is "vnd.android.cursor.item/sip_address".

It's pretty generic right now (basically a single text field, like
"Website") but we may eventually want to extend it later to have multiple
labels+types (like phone numbers.)

Bug: 2942998

Change-Id: I45d90a680a3badf60bccb5aafdc2397037494e95