Merge pull request #353 from ageery/wicket-6.x

Enhancement to annotation event dispatcher: unwrap and rethrow ReplaceHandlerExceptions
[jee-web] JSP tag supports EL in attributes (wicket-6.x)
Added a new overlay (rectangle) including example, two new events (mouseup, mousedown) and some documentation.
(cherry picked from commit 70b9249b772956618946f933af141ef8ad0db0d9)
[travis] Just test the pull requests, deploy commits
[travis] Improve the check whether the build is from a Pull Request
[travis] Add debug for DEPLOY_OR_TEST
Adde ajaxFormSubmit to submit forms via AJAX.
Merge remote-tracking branch 'origin/wicket-6.x' into wicket-6.x