Add rowstride to tiled rendering via LibLO.

The buffer width could be larger than the desired rendering
width, hence we need to give the client access to the rowstride.

Change-Id: Ic63c1f455c89960164e076ed2528d43e64e81a40
Implement document size retrieval for LibLO.

Change-Id: Ibd69f8e766fd421b05d2305f967179a969bc5b56
Draw the whole image for our gtk tiled viewer.

We just draw one huge tile, it doesn't seem to work too well
for larger documents though where the latter portions can appear
empty.

Change-Id: Ic527aec377bf2f82a528a04392186d3d8b752762