(bug 42198) fix ext.wikiEditor.publish so that it actually works

Two fixes:

* The Cancel button previously simply did nothing. However, since it's a
  button, it caused the form to be submitted - essentially saving the edit
  instead of cancelling it.

  Now it sets window's location to "Cancel" link's href (already present in
  vanilla MediaWiki) and cancels the submitting of the edit form.

* The Publish button did nothing as well (except that it cancelled the form
  submission). This was caused by the dialog it was supposed to show not being
  initialized.

  I simply forced its initialization using "immediateCreate: true".

Change-Id: I64589985b6075183e66eaa40bc457acbbae380b1
Merge "(bug 42198) fix ext.wikiEditor.publish so that it actually works"