Add "Switch Header/Source" action to the context menu

Task-number: QTCREATORBUG-5324

Change-Id: I137c9430e538714684ff6000ea68340a6f802615
Reviewed-on: http://codereview.qt.nokia.com/2688


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Leandro T. C. Melo <leandro.melo@nokia.com>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@nokia.com>