WICKET-5771 Ability to escape resource bundle messages added with
wicket:message
WICKET-5771 Ability to escape resource bundle messages added with wicket:message

Non functional improvements:
fix javadoc errors, cache and reuse local variable, extract constants for the attributes, Java 7 diamonds
WICKET-5772 set attached after load, so failuer of load() will not keep null value
WICKET-5774 UrlRenderer should render full and absolute urls in their canonical form
JavaDoc fixes, most of them for WICKET-5410 (All IXyzSettings are
removed)
WICKET-5759 AjaxRequestAttributes extra parameters aren't properly handled in getCallbackFunction()
WICKET-5759 AjaxRequestAttributes extra parameters aren't properly handled in getCallbackFunction()

Fix test expectations
WICKET-5775 Replace the session upon successful signin for better support for Session Fixation
WICKET-5771 Ability to escape resource bundle messages added with wicket:message

Copy wicket-1.5.xsd into wicket.xsd to make it usable even in versions newer than 1.5.x.
Set <schema> version attribute to 6.18.0. IMO we should update this with every change made in this file.
Add 'escape' attribute to <wicket:message> element.

(cherry picked from commit 920779a980d9873eb077652a2e20a45d168d15d9)
WICKET-5771 Ability to escape resource bundle messages added with wicket:message

Remove wicket-1.5.xsd.
Update version of wicket.xsd to 7.0.0
Remove obsolete DTDs
Remove a noop method from ChangeListenerSet. The class is final so it is not overridden by users
Fix the javadoc of Strings#getLevenshteinDistance()
Non functional:

- Java 7 diamonds
- inline member field as a local
WICKET-5778 Pass the IModifiable to the IChangeListener in ModificationWatcher

Introduce temporary interface IChangeListener2 that can be used when one needs the changed object as a parameter