Implement a (qa-only) quad-tiled viewer.

I.e. we subdivide the document into 4 tiles: one at 100% scaling,
one at 200%, one at 50%, one at 25% -- these are then post-scaled
in gdk) and assembled to show as one document again.

This is specifically a test only widget, primarily to be able to quickly
spot any tile positioning/border-transition issues.

We could theoretically make this widget inherit from the original widget,
however that would mean having to introduce virtual methods etc., which
is not something that we'd want in production -- in the longer run
that widget will hopefully be extended to have proper tile composition etc.,
which would then break this widget too if it were inheriting from there.

Change-Id: Ib880a1614f89724135e753013cf91aec25973e39
LOK DocView: only rerender on zoom if we have a document open.

Otherwise we would segfault, and it's perfectly valid to set a zoom
level _before_ opening a document (as that would e.g. save the document
first being rendered on opening if the client wants to immediately
render at a non-standard zoom level).

Change-Id: Ide261b09f4aab8dc3b552f6c3bf55f78ffd7870c
Quad Docview: only rerender on zoom if we have a document open.

Same as
"LOK DocView: only rerender on zoom if we have a document open."
but for our quad-tiled test widget.

Change-Id: I6c1b946cc9d576d1dcc4687048339d9f0b3e6eff
gtktiledviewer: allow selecting between normal and quad-tile view.

Change-Id: I85b22b93fe4ce2ffb62df8766ceea7a1bd8961ee
Add get/setPart to ITiledRenderable, and implement for sw/sc.

Change-Id: Iec3d6374f029149cadf8fb9c9b16fec90146c31e
LOK DocView: implement part selection.

Change-Id: I2e16ca9d2d5fcd25b0435f1b9b0fbcb52b92e012
Add part selector to gtktiledviewer.

Change-Id: I569c8f0ebf4476c0a247cde15a263d1db956a14b
Add Tiled Rendering outline to sd.

Change-Id: I810d827f330690f8071b662b9ddd05cc41655a71
Add LOK tiled rendering divided-tile unit test.

I.e. we render the same area as one larger tile, and then
as 4 sub-tiles (which, when put together, should be identical
to the larger tile). However currently only the top-left sub-tile
actually matches the larger tile, so we have to disable the test
for the remaining sub-tiles.

Change-Id: If1130022b43898e20fefff3e9f592102da3e413a
Add LOK and tiledrendering log areas.

Change-Id: I885acc9b4a52835fa256c2ecd1b8da917b4f7ba7
LOK: some logging for tiled rendering.

Change-Id: I5779eec97507b1996cda89174a6e6c55cdd57baf
LOK: use solar mutex for setPart.

Needed e.g. for changing slides in impress.

Change-Id: I2f5de40d4efbacde910e27225768979a98ff1c0a
Impress: implement tiled rendering.

However we cannot as of yet select between rendering just the slide,
just the notes, or both combined -- this simply defaults to whatever
mode the document was last opened in for now.

Change-Id: Ia8ec0280aab75a36e430aa04c47cee4fea2db974