Add intent broadcast when a PhoneAccount is enabled or disabled. (3/3)

- Handling intent in SipAccountRegistry and disabling/enabling Sip
accounts as required.
- Changing SipSettings so that disabled Sip account do not show as
"receiving calls" when they're disabled.

Bug: 17408536
Change-Id: Ia74c8c884719e8c399dfe6941980f467e00ac87b
5 files changed