XWIKI-5187: XWiki Explorer doesn't support very well spaces and pages with special characters in their names
* Extract the SmartClient library in the package mojo in order to have a functional tree in platform integration tests.
* Move SmartGWT version property from xwiki-platform-core to xwiki-platform root POM in order to have it available in the package plugin integration tests.
* Add page object for XWiki Explorer tree in xwiki-platform-test
* Move XWiki Explorer functional tests from xwiki-enterprise-test-selenium to xwiki-platform-index-test-tests
* Add functional test for special characters in space and page names.
* Parse the parent id as a document reference to support special characters in the page name, like @