Add gradle build file for Dialer

This CL adds gradle build files for Dialer. Currently the build file
in the InCallUI code only builds resources. Eventually we'll want to
make that a standalone library project.

Things missing from this CL:
  - support for src-N
  - build target for dialer-library to be included by GoogleDialer

Bug: 26676586
Change-Id: Ie91cb720cf17fd8579b04a01287e140b39d0c42f