first iteration on 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("rosandroid", RosAndroidPluginExtension)
+        project.rosandroid.buildToolsVersion = "17"
+    }
+}
+
+class RosAndroidPluginExtension {
+    String buildToolsVersion
+}

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

@@ -35,6 +35,10 @@ class RosPlugin implements Plugin<Project> {
                 }
             }
         }
+        /* 
+         * Could use some better handling for when this is not defined as it sets
+         * file://null, but it doesn't seem to hurt the process any
+         */
         def repoURLs = project.ros.mavenPath.collect { 'file://' + it }
         project.repositories {
             repoURLs.each { p ->

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

+implementation-class=org.ros.gradle_plugins.RosAndroidPlugin
\ No newline at end of file