XWIKI-5187: XWiki Explorer doesn't support very well spaces and pages with special characters in their names
* Use the serialized space reference as space identifier instead of hardcoding the wiki-space separator.
* Encode the URL path components when building the REST URL to support entities that have special characters in their name.
* Escape the RegExp special characters from the submitted parent id because the REST server uses the parent id as a regular expression.