[Android-tools-devel] Bug#819074: Bug#819074: point gradle to plugins

[殷啟聰]

All built-in plugins are included in the Gradle project, it does not
need to download the plugins when using.

But one still needs to download custom plugins. Before
gradle-debian-helper, packages in Debian also needs to specify the
local Maven repo URL.

I think it would be a bad idea to integrate the Android plugin into
Gradle itself, because it is just not part of Gradle. Maybe we can
have something like gradle-debian-helper but for Android applications?
A.k.a, "android-debian-helper"?