Add application category for OS X

The Applications folder in OS X is large and installers tend to expect apps to stay where they were placed (i.e. the root of /Applications). Since Lion, there's been application category metadata for View --> Arrange by Application Category but if the metadata's not in info.plist, the app gets sorted into "Other" at the bottom. 

https://developer.apple.com/library/Mac/releasenotes/General/SubmittingToMacAppStore/#//apple_ref/doc/uid/TP40010572-CH16-SW8 (this applies to all Mac apps, not just those installed through App Store).
Merge pull request #324 from duanemoody/master

Add application category for OS X