fdo#72420 Startcenter: help button point to local/wiki help, ui part

Change-Id: I7ac4b51868d1a5828c810b1ac629d5a56ffb6f50
fdo#72947 Startcenter: display more userfriendly file urls in tooltips

Use INetURLObject to get a readable url (it displayes special characters
too). It is a side effect that 'file:///' prefix disappear
which seems a good thing.
Plus some cleanup: remove second INetURLObject.

Change-Id: I4aab5e2546ae70e5a3d85b12e26e021bfa244999