Added Gradle build files because Ant's too efficient for some people.

briar-core/build.gradle

@@ -0,0 +1,12 @@
+apply plugin: 'java'
+
+dependencies {
+    compile fileTree(dir: '../briar-api/libs', include: '*.jar')
+    compile project(':briar-api')
+    compile fileTree(dir: 'libs', include: '*.jar')
+}
+
+sourceSets {
+    main.java.srcDirs = ['src']
+    main.resources.srcDirs = ['src']
+}