Fix property sheet error in labelMorph on Mac OS X
This fixes #4. On Mac OS X the 'scalableFont' property does not
exist in the windowCanvas for quartz. This adds it by falling
back on the X11 implementation.

This commit also adds a 'verdana' font entry to the list of X11
fonts allow Verdana to display and be selected in the property
sheet. On Mac OS X this correctly results in Verdana displaying.
On Linux without Verdana it falls back to the default, Times.