Adds help popup

src/main/java/io/bitsquare/gui/help/Help.java

@@ -0,0 +1,56 @@
+package io.bitsquare.gui.help;
+
+import io.bitsquare.BitSquare;
+
+import java.net.MalformedURLException;
+import java.net.URL;
+
+import javafx.scene.*;
+import javafx.scene.web.*;
+import javafx.stage.Modality;
+import javafx.stage.Stage;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+// TODO Find good solution for a web based help content management system. 
+public class Help {
+    private static final Logger log = LoggerFactory.getLogger(Help.class);
+
+    private static Stage helpWindow;
+
+    ///////////////////////////////////////////////////////////////////////////////////////////
+    // Public methods
+    ///////////////////////////////////////////////////////////////////////////////////////////
+
+    public static void openWindow(HelpId id) {
+        try {
+            URL url = new URL("https://github.com/bitsquare/bitsquare/wiki/?" + id);
+            WebView webView;
+            if (helpWindow == null) {
+                helpWindow = new Stage();
+                helpWindow.initModality(Modality.NONE);
+                helpWindow.initOwner(BitSquare.getPrimaryStage());
+                webView = new WebView();
+                webView.getEngine().load(url.toString());
+                Scene scene = new Scene(webView, 800, 600);
+                helpWindow.setScene(scene);
+                helpWindow.onCloseRequestProperty().addListener((ov, oldValue, newValue) -> {
+                    if (oldValue != null && newValue == null)
+                        helpWindow = null;
+                    log.debug("closed");
+                });
+
+                helpWindow.show();
+            }
+            else {
+                webView = (WebView) helpWindow.getScene().getRoot();
+            }
+            helpWindow.setTitle(url.toString());
+            webView.getEngine().load(url.toString());
+        } catch (MalformedURLException e) {
+            log.error(e.getMessage());
+        }
+    }
+
+}

src/main/java/io/bitsquare/gui/help/HelpId.java

@@ -0,0 +1,8 @@
+package io.bitsquare.gui.help;
+
+public enum HelpId {
+    CREATE_OFFER_GENERAL,
+    CREATE_OFFER_FUNDING,
+    CREATE_OFFER_ADVANCED
+
+}