MiniBrowser::processDidCrash reimplemented to reuse NIXView instance

* MiniBrowser's callback function "processDidCrash" rewritten to reuse
  NIXView instance created when it is initialized, instead of deallocate
  and create a new instance as was being done in its previous implementation

* TRICK: NIXView was initializing its "CoordinateGraphicsScene" only
  in its "initialize" method, so when web process crashes - and we
  reuse NIXView instance, only reloading previous loaded page - we need
  to reactivate CoordinateGraphicsScene explicitily

Signed-off-by: Nick Diego Yamane <nick.yamane@openbossa.org>

Reviewed by: Jesus Sanchez-Palencia