Add application category for OS X

Because OS X apps generally don't like apps being subfoldered (updates miss their targets), as of Lion the Finder has had an Applications-specific View by Application Category view. It sorts by a piece of metadata called LSApplicationCategoryType which if missing, dumps the application in the "Others" section at the bottom. This commit adds the correct application category for FontForge, "Graphics & Design".
Merge pull request #1350 from duanemoody/master

Add application category for OS X