support for permalink and external url

Consolidate GetURL AppleEvent handling into AppDelegate+Scriptability
file
Add scripting access groups to sdef
Add exists command
Add ‘permalink’ and ‘external url’ properties to the article scripting
object
Add a unit test to verify the behavior of ‘current article’

EvergreenTests/ScriptingTests/scripts/testURLsOfCurrentArticle.applescript

@@ -0,0 +1,14 @@
+-- this script   tests that it is possible to get the url property of the current article
+-- it uses system event accessibility scripting to set up the main window
+-- one needs to authorize scripting accessibility control in the System Preferences'
+--  Privacy and security pane
+
+try
+    tell application "Evergreen"
+        {url, permalink, external url} of current article
+    end tell
+on error message
+	return {test_result:false, script_result:message}
+end try
+
+return {test_result:true, script_result:"tests passed"}