Task-number: QTCREATORBUG-2335

 - lessens open file handles
 - improves help plugin startup further

Task-number: QTCREATORBUG-337
Reviewed-by: ck

Also removed a superfluous elide mode setter.

Reviewed-by: kh1

Reviewed-by: ck

Make Thorbjorn happy.  :)

Reviewed-by: ck

Since we use a two column model/treeview we need to prevent returning
some text data, otherwise we will see dots in the secound column. We also
need to emit pagesChanged once we init the model.

Based on the implementation done by ck, slightly modified and thus put
under the private help internal namespace.