Implements the "Properties" menu item which displays the preferences window

Implements the "Properties" menu item which displays the preferences window
at the correct notebook page when a particular protocol (which has registered
some preferences) is selected in the tree view.

- add set_menus_for_selected_tree_row() in menu.[ch]

- add prefs_is_registered_protocol() and
      prefs_get_title_by_name() in prefs.[ch]

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@2275 f5534014-38df-0310-8fa8-9805f1628bb7