#50 Assume notray in server mode

[niol]

This is to work around the following failure when using openjdk-headless.

 Exception in thread "main" java.awt.AWTError: Assistive Technology not found: org.GNOME.Accessibility.AtkWrapper
        at java.awt.Toolkit.loadAssistiveTechnologies(Toolkit.java:807)
        at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:886)
        at java.awt.SystemTray.isSupported(SystemTray.java:219)
        at davmail.ui.tray.DavGatewayTray.init(DavGatewayTray.java:233)
        at davmail.DavGateway.main(DavGateway.java:80)

--- davmail.git.orig/src/java/davmail/DavGateway.java   2018-10-18 12:03:04.251708743 +0200
+++ davmail.git/src/java/davmail/DavGateway.java    2018-10-18 15:11:10.816463983 +0200
@@ -77,7 +77,10 @@
             Settings.setProperty("davmail.server", "true");
             Settings.updateLoggingConfig();
         }

-        DavGatewayTray.init(notray);
+
+        if (!Settings.getBooleanProperty("davmail.server")) {
+            DavGatewayTray.init(notray);
+        }

         start();

[Mickael Guessant]

Merged in trunk, thanks for your contribution