CMS-3488 Introduce UI Framework for responsive layout

Implemented UI framework for the size ranges.
Added ResponsiveManager utility class to listen for the global resize
events.
Added ResponsiveItem class, that manages responsive classes.
Updated SplitPanel class.
Updated ContextWindow class.
Merge pull request #745 from enonic/CMS-3488

CMS-3488 Introduce UI Framework for responsive layout