Implement start screen logic

app/src/main/res/values/strings.xml

@@ -3,4 +3,5 @@
     <string name="label_server">Server</string>
     <string name="label_info">This screen will be shown only once. After you click the button, server address will be saved in preferences. To change it, clear app data from application manager.</string>
     <string name="button_start">Start</string>
+    <string name="error_connection">Server connection failed</string>
 </resources>