Refactor ve.ui.PagedDialog

This commit extracts the page and outline handling logic from
ve.ui.PagedDialog (RIP) and moves it into two layouts: ve.ui.PagedLayout
and ve.ui.PagedOutlineLayout, respectively. These layouts are now implemented
inside the dialogs that used to mixin the ve.ui.PagedDialog class. This
brings a much cleaner separation of concerns between Dialogs and Layouts
and allows the use of page handling logic without the accompanying
outline logic.

Change-Id: I5efa2f893f4b7e962438b3aff34b737573bbd5ca
Merge "Refactor ve.ui.PagedDialog"