NFC: Host-based card emulation APIs.

- New INfcCardEmulation interface to allow apps to interface
  with card emulation system.
- New BIND_NFC_SERVICE permission to prevent malicious apps
  from binding to card emulation services.
- ApduServiceInfo is now in the framework.
- Added constants to Settings.Secure for storing defaults.
- Modified XML grammar a bit.

Change-Id: I56b3fa6b42eb5dc132c91c1386ab1e6bac779059