Various updates to support IDEA

Remove the 'final' modifier from SingletonBeanFactoryLocatorTests
to work around the "cannot extend final class" error issued when
running all tests. The error was due to confusion with IDEA between
the two variants of SingletonBeanFactoryLocatorTests across
spring-context and spring-beans.

Rename one of the GroovyMessenger classes to GroovyMessenger2.
Previously there were multiple Groovy classes named
'GroovyMessenger', causing a compilation error in certain IDE
arrangements.

Update import-into-idea.md documentation

Add various IDEA artifacts to .gitignore
 - ignore derby.log wherever it is written
 - ignore IDEA's test-output directory
 - ignore IDEA's Atlassian connector config file

spring-context/src/test/java/org/springframework/scripting/groovy/Messenger.groovy

@@ -1,8 +1,7 @@
 package org.springframework.scripting.groovy;
 
-import org.springframework.scripting.ConfigurableMessenger
 import org.springframework.stereotype.Component;
 
 @Component
-class GroovyMessenger extends ConcreteMessenger {
+class GroovyMessenger2 extends ConcreteMessenger {
 }