Issue #34

- extended CASStylebaleItem with the cas_styleClasses property which will hold a set of style classes
- setter of cas_styleClass now set the cas_styleClasses and is just an alternative to set the cas_styleClasses, it supports also setting multiple classes by separating them with CASStyleClassSeparator (which is currently one whitespace)
- update CASStyleSelector to utilise the cas_StyleClasses set for comparison
- updated related +CASAdditions with support for multiple classes
- removed unused methods in NSString+CASAdditions.h
Merge branches 'feature/MultipleClasses' and 'feature/MultipleClasses' of https://github.com/Ajax64/Classy into feature/MultipleClasses