Add FindGradle from KNotification
Besides finding Gradle from QtAndroidExtras and thus avoiding the usual way of the Android world of distributing that (a copy in your source code), it provides macros to generate and install Android AARs. Those are needed for libraries that have a non-trivial Java component on Android, e.g. needing a manifest fragment or having a dependency on other Java libs.
This file has been copied to a few places meanwhile, so centralizing this in ECM makes sense.