Add S-NSSAI

* Added support for S-NSSAI
* Created SliceInfo that represents a S-NSSAI as defined in
  3GPP TS 24.501.
* Added slice info to setupDataCall and DataCallResponse within
  DataService related classes

Bug: 169960538
Test: made ims phone call
Change-Id: I8f136937f127ff14fedd790526544d5775010da8