webif: Reword shutdown page.

Reword and also replace urlencoded symbols with normal ones.

' (single quote) and / (slash) do not need to be urlencoded when
used in normal text paragraph.

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@9236 4b0bc96b-bc66-0410-9d44-ebda105a78c1