Simplified and cleaned up code

This also prepares the removal of the deprecated method SMWWikiPageValue::getSortKey().
This change does not affect functionality or behaviour.
Initialisation code for formatting parameters was moved to own method.
Otherwise, no new methods have been introduced, but some were renamed (hence the @since 1.9 tags).

Change-Id: If48871c8e1035d53f3cbf814a5f174b1c8057e72