qt-brisa: change qobjects cleanups policy

we have these objects:

httpserver (main thread) :
  httpsessionmanager (#1 thread)
      httpsession
      httpsession
  httpsessionmanager (#2 thread)
      httpsession
      httpsession

so, these objects belongs to these threads:

 main thread:
   httpserver
   httpsessionmanager

 #N thread
   httpsession

To remove httpsession correctly httpsessionmanager must be stopped.

Signed-off-by: Rouming <rouming>
qt-brisa: we should explicitly stop web server before clearing services
qt-brisa-mediaserver: add 'browse' handle skeleton
qt-brisa: change logic of handling main brisa device description requests

GET /device_name.xml HTTP/1.0

brisa should response with xml which describes this device.
this xml is being generated only once.
previously brisawebfile was used to return its content.
this patch changes brisawebfile on brisawebstaticcontent,
because this xml is actually a buffer, not a file.

also use setContentType(text/xml) as default type for
this xml.
qt-brisa: set default web server response as text/plain

also implement handy function for httpmessage which says
cotains this message some header or not.

use this function for setting default content-type of http response.
default type is: text/plain.
this type will be set if other classes in stack skipped this header.
qt-brisa: some garbage cleanups