Add activator to enable loading resources from other plugins

* The DSE perspective has a HelpView that provides context-sensitive
  help

Issue-Ref: 3829
Issue-Url: https://af3-developer.fortiss.org/issues/3829



Signed-off-by: Simon Barner <barner@fortiss.org>

org.fortiss.af3.rcp.help/.classpath

@@ -6,5 +6,6 @@
 		</attributes>
 	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.pde.core.requiredPlugins"/>
+	<classpathentry kind="src" path="src"/>
 	<classpathentry kind="output" path="build"/>
 </classpath>

org.fortiss.af3.rcp.help/META-INF/MANIFEST.MF

@@ -9,4 +9,6 @@ Bundle-RequiredExecutionEnvironment: JavaSE-11
 Bundle-ActivationPolicy: lazy
 Require-Bundle: org.eclipse.help.ui;bundle-version="4.1.500",
  org.eclipse.help.webapp;bundle-version="3.9.500"
+Export-Package: org.fortiss.af3.rcp.help
+Bundle-Activator: org.fortiss.af3.rcp.help.AF3HelpActivator
 

org.fortiss.af3.rcp.help/build.properties

 # (c) 2019 fortiss GmbH
 
+source..     = src/
 bin.includes = plugin.xml,\
                META-INF/,\
                .,\

org.fortiss.af3.rcp.help/src/org/fortiss/af3/rcp/help/.ratings

+AF3HelpActivator.java ba9e079aa36be2c09780df324cdca9fcd280711e YELLOW

org.fortiss.af3.rcp.help/src/org/fortiss/af3/rcp/help/AF3HelpActivator.java

+/*-------------------------------------------------------------------------+
+| Copyright 2019 fortiss GmbH                                              |
+|                                                                          |
+| Licensed under the Apache License, Version 2.0 (the "License");          |
+| you may not use this file except in compliance with the License.         |
+| You may obtain a copy of the License at                                  |
+|                                                                          |
+|    http://www.apache.org/licenses/LICENSE-2.0                            |
+|                                                                          |
+| Unless required by applicable law or agreed to in writing, software      |
+| distributed under the License is distributed on an "AS IS" BASIS,        |
+| WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
+| See the License for the specific language governing permissions and      |
+| limitations under the License.                                           |
++--------------------------------------------------------------------------*/
+package org.fortiss.af3.rcp.help;
+
+import org.eclipse.jface.resource.ImageDescriptor;
+import org.eclipse.ui.plugin.AbstractUIPlugin;
+import org.osgi.framework.BundleContext;
+
+/**
+ * Activator class for AF3 RCP Help
+ * 
+ * @author barner
+ */
+public class AF3HelpActivator extends AbstractUIPlugin {
+
+	/** The ID of this plug-in. */
+	public static final String PLUGIN_ID = AF3HelpActivator.class.getPackage().getName(); // $NON-NLS-1$
+
+	/** The shared instance. */
+	private static AF3HelpActivator plugin;
+
+	/** {@inheritDoc} */
+	@Override
+	public void start(BundleContext context) throws Exception {
+		super.start(context);
+		plugin = this;
+	}
+
+	/** {@inheritDoc} */
+	@Override
+	public void stop(BundleContext context) throws Exception {
+		plugin = null;
+		super.stop(context);
+	}
+
+	/** Returns the shared instance. */
+	public static AF3HelpActivator getDefault() {
+		return plugin;
+	}
+
+	/** Returns an image descriptor for the image file at the given plug-in relative path. */
+	public static ImageDescriptor getImageDescriptor(String path) {
+		return imageDescriptorFromPlugin(PLUGIN_ID, path);
+	}
+}