Readloop remove special cases

Readloop remove special cases

  - add handler for initializing the page
  - add parameter to handler GetParamsGetServerCall() so clients can register a list filter to MSG4
  - Json-view: use new initialisation handler to output the headers for the JSon-reply
  - Json-view: don't need the extra member on the session anymore.
  - Json-View: split functions into wrapper page and json list
  - wiki-view: register empty header output handler, since the sub-calls do this later.
  - wiki-view: use the GetParamsGetServerCall()-Callback to hook in our logic instead of tainting readloop() with special code.