Add the ScopedModel Counter sample (#41)

Adds sample app that mimics the beloved starter app, but with ScopedModel for state management.

Contains a smoke test and is set up to run it in travis_script.sh.

scoped_model_counter/android/settings.gradle

@@ -0,0 +1,15 @@
+include ':app'
+
+def flutterProjectRoot = rootProject.projectDir.parentFile.toPath()
+
+def plugins = new Properties()
+def pluginsFile = new File(flutterProjectRoot.toFile(), '.flutter-plugins')
+if (pluginsFile.exists()) {
+    pluginsFile.withReader('UTF-8') { reader -> plugins.load(reader) }
+}
+
+plugins.each { name, path ->
+    def pluginDirectory = flutterProjectRoot.resolve(path).resolve('android').toFile()
+    include ":$name"
+    project(":$name").projectDir = pluginDirectory
+}