[Qt] add utilitydialog.cpp/h and helpmessage class

- adds a nice and well formated dialog, which displays our -? help message
  (all options/paramaters)
- moves aboutdialog.cpp/h to the new utilitydialog
- move GUI shutdown window to utilitydialog

contrib/bitcoin-qt.pro

@@ -4,6 +4,7 @@ FORMS += \
     ../src/qt/forms/askpassphrasedialog.ui \
     ../src/qt/forms/coincontroldialog.ui \
     ../src/qt/forms/editaddressdialog.ui \
+    ../src/qt/forms/helpmessagedialog.ui \
     ../src/qt/forms/intro.ui \
     ../src/qt/forms/openuridialog.ui \
     ../src/qt/forms/optionsdialog.ui \