Paged dialog upgrades

Objective:

* Add functionality to paged dialogs to work with the pages and select
  them programmatically

Changes:

ve.ui.PagedDialog.js
* Keep track of the current page name
* Add setPage method, which is can be used publicly and is also used
  internally when items in the outline are selected
* Add a page content config option which auto-appends to the inside of
  the page
* Add removePage method for removing pages by name
* Add getPageName method which gets the current page name

Change-Id: I2a2f0c329d274796b8c9e7572ecff8294f472f7f
Merge "Paged dialog upgrades"