gradle: fix vtm-android install + generate source jars

vtm-themes/build.gradle

@@ -10,3 +10,11 @@ sourceSets {
   main.java.srcDirs = ['src']
   main.resources.srcDirs = ['resources']
 }
+
+task sourcesJar(type: Jar, dependsOn: classes) {
+  classifier = 'sources'
+  from sourceSets.main.allSource
+}
+artifacts {
+  archives sourcesJar
+}