ros android plugin

gradle_plugins/src/main/groovy/org/ros/gradle_plugins/RosAndroid.groovy

+package org.ros.gradle_plugins;
+
+import org.gradle.api.Project;
+import org.gradle.api.Plugin;
+import org.gradle.api.*;
+
+/*
+ * Configures java for the ros-android build environment. Pretty elementary right now,
+ * just applies the java plugin and defines the jdk compatibility level.
+ */
+class RosAndroidPlugin implements Plugin<Project> {
+    Project project
+    
+	def void apply(Project project) {
+	    this.project = project
+        if (!project.plugins.findPlugin('ros')) {
+            project.apply(plugin: 'ros')
+        }
+        project.extensions.create("ros.android", RosAndroidPluginExtension)
+        project.ros.android.buildToolsVersion = "17"
+    }
+}
+
+class RosAndroidPluginExtension {
+    String buildToolsVersion
+}

gradle_plugins/src/main/resources/META-INF/gradle-plugins/ros-android.properties

+implementation-class=org.ros.gradle_plugins.RosAndroidPlugin
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