ConTeXt template: add a saner default for page numbers.

Previously they appeared centered at the top of the page;
now we put them centered at the bottom, unless the `pagenumbering`
variable is set (this gives users full control over page
number format and position,
https://wiki.contextgarden.net/Command/setuppagenumbering)

data/templates/default.context

@@ -36,6 +36,8 @@ $if(layout)$
 $endif$
 $if(pagenumbering)$
 \setuppagenumbering[$for(pagenumbering)$$pagenumbering$$sep$,$endfor$]
+$else$
+\setuppagenumbering[location={footer,middle}]
 $endif$
 $if(pdfa)$
 % attempt to generate PDF/A

test/writer.context

@@ -11,6 +11,7 @@
 \placebookmarks[chapter, section, subsection, subsubsection, subsubsubsection, subsubsubsubsection][chapter, section]
 \setupinteractionscreen[option=bookmark]
 
+\setuppagenumbering[location={footer,middle}]
 \setupbackend[export=yes]
 \setupstructure[state=start,method=auto]
 

test/writers-lang-and-dir.context

@@ -9,6 +9,7 @@
 \placebookmarks[chapter, section, subsection, subsubsection, subsubsubsection, subsubsubsubsection][chapter, section]
 \setupinteractionscreen[option=bookmark]
 
+\setuppagenumbering[location={footer,middle}]
 \setupbackend[export=yes]
 \setupstructure[state=start,method=auto]