A bit different approach than trying to paint different zoom levels at
the samet time, because it is terribly hard to achieve with Calc -
things misalign, because Calc tries to fit the lines into the pixels
etc.

Instead, always paint the spreadsheet at 100%, but use cairo to scale the
actual painting.

Change-Id: I228a9dd41bf29862bdd188825d12e61e1c86cccc