Add ITiledRenderable.

We want to have a simple interface that allows access to tiled
rendering without digging into the internals of writer
(and in the future calc/impress/draw).

Change-Id: Ia9c278a48c919333186e5361ff25bb1ab603b846
Use ITiledRenderable for LIBLOK.

Means that no changes should be required here once calc/impress/draw
support tiled rendering.

Change-Id: I0987d94303f39ba37e29b9ae7b2276e82dc0ccbf