add a descriptive suffix to all the different kinds of constants for easy visual identification

I found i was typing these suffixes all the time anyway so I chose to add them automatically. This makes it so that i can put "viewDetail" in the segue identifier box in IB and it gets generated as XXXViewDetailSegue in the constants, for example
Added forward declaration of class used for constants as in modern projects there is no prefix header to import foundation
Merge branch 'suffix-generation' of github.com:joelparsons/storyboard-constants