put unit tests into external module (CAVEAT)

this requires a more up to date version of gradle-android-test-plugin
than is currently in the repositories. it must be added to the local
maven repo using ./install-custom-gradle-test-plugin.sh before
compiling.

install-custom-gradle-test-plugin.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+
+mkdir temp
+cd temp
+
+  git clone https://github.com/nenick/gradle-android-test-plugin.git
+  cd gradle-android-test-plugin
+
+    echo "rootProject.name = 'gradle-android-test-plugin-parent'" > settings.gradle
+    echo "include ':gradle-android-test-plugin'" >> settings.gradle
+
+    ./gradlew :gradle-android-test-plugin:install
+
+  cd ..
+cd ..