Fixes#750
Currently, Keyman for Android targets SDK version 25 (Nougat).
This PR targets the latest Android API and updates all the Gradle dependencies to the latest. This will remove some lint Obsolete warnings.
Sample and Test projects needed to add
```
implementation 'com.android.support:support-v4:27.1.1'
```
to ensure all dependencies use the same version.
Per Android Studio 3.0 [Release Notes](https://android-developers.googleblog.com/2017/10/android-studio-30.html)
-Update gradle version
-Change deprecated `compile` dependencies to `implementation` or `api`
-Change maven repositories to google (triplet plugin still on maven)
- Update readme instructions for using the engine