replace 'recess' and 'less' references and tasks with same for sass

In addition, it fixes the characters that throw errors on compile in lib/_grid.scss, and removes Recess for grunt-contrib-sass.  Compass seems like overkill if we just want to make a task that is equivalent to the original Recess compile.  You will notice that the precision of calculations in the compiled CSS files (dist/css) are less than that of the original, as compiled from LESS.  Precision can be adjusted in the 'sass' task options in the Gruntfile, if deemed necessary (default is 3).  I also registered a 'watch-sass' task which just calls 'watch:sass'.