Build the live table results in memory to be able to make adjustments before JSON serialization

XWiki.LiveTableResults page is currently using macros from XWiki.LiveTableResultsMacros which print the JSON directly to the response. This makes it very hard to have a custom JSON that only changes a few properties or adds new ones. The current practice is to copy the code from XWiki.LiveTableResultsMacros and modify it but this makes the live table hard to maintain.