Add a view-only iOS test app using tiled rendering

I had to add some horrible hacks to make sure the test doc has been
loaded into a Writer shell before retrieving its size and being able
to render it. Obviously some better solution is needed. But this is
just a testbed to get some profiling data.

The app is built using an Xcode project, and in gbuild through a
custom target based on the MobileLibreOffice one. Setting up the
various files used (or not used...) at run-time should really be
factored out from the CustomTarget files.

Change-Id: I1711b0cae9d28a09b73476b2d37d98b1820c9943