Introduce ViewLoaderTest and FxmlResource interface

Tests basic loading of FXML resources via the ViewLoader API. Also
introduces the FxmlResource abstraction, an interface which the
Nagivation.Items enum now implements. This simplifies the process of
testing, e.g. in this case testing a non-existent resource without
having to add a bogus value to the enum itself.

Note the @BeforeClass logic necessary to initialize the JavaFX platform.
This is necessary in order to avoid "Toolkit not initialized"
exceptions. See http://stackoverflow.com/q/11385604 for details.

src/test/java/io/bitsquare/util/ViewLoaderTest.java

@@ -0,0 +1,75 @@
+/*
+ * This file is part of Bitsquare.
+ *
+ * Bitsquare is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Bitsquare is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Bitsquare. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package io.bitsquare.util;
+
+import io.bitsquare.FatalException;
+import io.bitsquare.di.BitsquareModule;
+import io.bitsquare.gui.Navigation;
+
+import com.google.inject.Guice;
+import com.google.inject.Injector;
+
+import javafx.application.Application;
+import javafx.stage.Stage;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class ViewLoaderTest {
+
+    public static class TestApp extends Application {
+        @Override
+        public void start(Stage primaryStage) throws Exception {
+        }
+    }
+
+    @BeforeClass
+    public static void initJavaFX() {
+        Thread t = new Thread("JavaFX Init Thread") {
+            public void run() {
+                Application.launch(TestApp.class);
+            }
+        };
+        t.setDaemon(true);
+        t.start();
+    }
+
+
+    @Before
+    public void setUp() {
+        Injector injector = Guice.createInjector(new BitsquareModule());
+        ViewLoader.setInjector(injector);
+    }
+
+    @After
+    public void tearDown() {
+        ViewLoader.setInjector(null);
+    }
+
+    @Test(expected = FatalException.class)
+    public void loadingBogusFxmlResourceShouldThrow() {
+        new ViewLoader(() -> "a bogus fxml resource", false).load();
+    }
+
+    @Test
+    public void loadingValidFxmlResourceShouldNotThrow() {
+        new ViewLoader(Navigation.Item.ACCOUNT, false).load();
+    }
+}