Refactor Utils#parseTemplate to use proper components

Utils#parseTemplate allows to parse a template and send the results in the request response with lots of stuff already performed as part of the process, such as taking into account the cache, resolving javascript placeholders, etc.
It's currently used in all the XWikiAction and it's quite easy to use it.
However since it's not a component it's difficult to unit test properly the components using it, so we should refactor it to improve our testing when using it.