This is the first form that uses HTMx, and can not return a 400 error
code because otherwise HTMx does not render the content.
Since now there are pages that do not render the whole html, with header
and body, i need a different layout for these, and moved the common code
to handle forms and such a new template file that both layouts can use.
I also need the request in template.MustRender to check which layout i
should use.
Closes#7.
