Update Gradle build and subsequent configuration for Android 7

- Add Google's Maven repository required by the newer Gradle for
  Android plugin version;
- Update Gradle wrapper (and include the source to benefit from the
  IDE integration) with:
  $ ./gradlew wrapper --gradle-version 4.4 --distribution-type all
- Add a lint hint to discard the warning about the target SDK version
  not being the latest one

Issue: FP2N-138
Change-Id: I542d93734204d892e9c87d164cbc1dde9650fa9e
6 files changed