Apparently the top/bottom line of text alignment in writer is backwards
compared to all others, while alignment to the top of a page puts
an object's top edge at the top of the page, top of line of text
puts the object on top of the line (i.e. bottom edge of the object
at the line). The handling of NS_rtf::LN_YAlign suggests that swapping
bottom and top in the input filter is the right way of handling this.

Change-Id: I916c8ea0f2fd00de3e17b16b31433c9b6ba92e64