add Akonadi::CollectionPropertiesDialog::setCurrentPage()

Review Request #106623 - Created Sept. 28, 2012 and submitted - Latest diff uploaded

Jonathan Marten
When a CollectionPropertiesDialog is opened, it always shows the first tab page.  In some applications it may be useful to request that the dialogue opens with a specific tab shown, for example if any formerly separate dialogues were to be merged into KMail's "Folder Properties" dialogue.  The action which summoned the original dialogue can remain in the GUI, which will open the combined dialogue with the appropriate tab shown.

This will hopefully reduce user confusion (of the "where has this gone from the menu?" variety).

This change (adding a new non-virtual function) is BC according to
Built kdepimlibs with this change, and added a testing stub to KMail to call it.  Verified that the specified tab page of the dialogue is shown when it is opened.