Make sure images that don't have an explicit alignment get aligned right

Make sure images that don't have an explicit alignment get aligned right

If the alignment of an image is not explicitly set, Parsoid does not
output an alignment class for the resultant figure element. This can lead
to the image not being aligned/floated.

To fix this we modify content.parsoid.less to apply the default
right-alignment styling to all images and then override this in cases
where the alignment is explicitly set.

Bug: 66282

Change-Id: I4f986f23b0c8ba6f6b66efc07eb38806744123e2