wmaker: Add more directions for window snapping.

This patch adds the ability to "snap" a window to the top, bottom, or any of the
four corners of the screen.  It uses three new helper functions, drawSnapFrame,
getSnapDirection, and doSnap, to reduce code duplication and increase
readability.

It also updates NEWS to indicate the additional directions.
wmaker: Consistent whitespace in WindowMaker.h.

Previously, the whitespace in WindowMaker was inconsistent, with some
indentation using spaces and some using tabs, and a mixture of tabs and spaces
used to align comments at the ends of lines.  As a result, patches that touched
this file would often result in warnings from checkpatch.pl.

This patch fixes this so that indentation uses tabs and all other alignment uses
spaces.