The menu is now displayed inside window, even when window
is not in fullscreen.
It now also contains the most important actions in addition to copy of
top level menus.
* move helper-functions in navigationbar.cpp into NavigationBar [private]
* remove (unused) 2nd arg in WebSearchBar/NavigationBar and use mainClass as parent.
* remove NavigationBar-destructor (not needed)
* remove WebSearchBar::m_menu and create a QMenu-instance directly in WebSearchBar::contextMenuEvent()
