Model, sidebar view refactoring, adding SxS sidebar handling

RegsData -> MetaModel, RegModel
Introduced FolderModel
RegsView -> SidebarModuleView
Introduced SidebarListView, SxSListView
RegsDispatch -> Dispatch

SxS sidebar list updates with section content
Sidebar definitions mostly work, need to recover the tab-activated close link. Important to get this changeset in, though, because of so many structural changes.