HTMX code as disscused in issue 686

[fastbike]

Added HTMX helpers for MVCWebRequest/Response
Added sample application

#686

[danieleteti]

I did some tests OK, we can put the sample in the official samples.
However, I removed Spring4D references because otherwise the sample was not compilable without having Spring4D which is not the point of the sample. Also, I think the MVCFramework.HTMX.pas should go in the sample folder and not in the source folder. I'll do the push ASAP.
Thank you

[fastbike]

Apologies for leaving the Spring4D references - you would have seen from the FB discussion I was playing around with how to simplify the scaffolding around the use of TObjectList structures.