Possibility to load page names inside Storyboard as a runtime attribute

Hi! Interesting project! I added a little convenience, by allowing to set a runtime attribute called pages with a comma separated string such as "page1, page2, page3, page4" that can be used instead of pageIdentifiers (it is used only if not overridden in a subclass). This further decouples the .m file from the Storyboard, and in most simple cases avoids subclassing of MSPageViewController at all.