iOS tiled rendering work

Possibly quite broken intermediate commit. But anyway, now it is
possible to render the tile diretly to a CGContext. Can be seen in
the MobileLibreOffice app when build in the Debug_tile_tester
configuration. See touch_lo_draw_tile() in viewsh.cxx. Unfortunately
the old plain LibreOffice test app is now broken, though, and
displays nothing at all.

This refactoring and hacking in vcl was done in a quite ugly fashion,
with ifdefs etc. But trust me, I did try, several times, for many
days, to get where I wanted in an elegant and clean fashion. But doing
it cleanly meant not being able to actually build it for days while
trying to figure ut which bits go where and which class should be
split into what base and derived class(es), and it was too much for my
limited brain capacity. I just couldn't juggle all the vcl class
structure in my head, especially as I don't have any good
understanding of the general design of it all.

Change-Id: Ia59d6a9cce15a63e63f94e8d8574bef21993fb1f