Enable specifying custom SDK and Build Tools versions

[DimiTech]

This solves APK building problems that arise due to differing SDK and Build Tools versions of the Root project and 'react-native-config'.

Without this, Android apps that use this dependency cannot be built, throwing the following error:

Warning: The rule `-keep public class *extends java.lang.annotation.Annotation {
  *;
}` uses extends but actually matches implements.
/Users/dusan-mitipi/.gradle/caches/transforms-1/files-1.1/appcompat-v7-26.1.0.aar/8e5c28697d7a976e3f3189250ef54cfd/res/values-v26/values-v26.xml:13:5-16:13: AAPT: No resource found that matches the given name: attr 'android:keyboardNavigationCluster'.

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':react-native-geocoder:verifyReleaseResources'.
> com.android.ide.common.process.ProcessException: Failed to execute aapt