Remember last values used in exec sample "Kill" menu item dialogs.

Remember last values used in exec sample "Kill" menu item dialogs.

Remember the PID entered in the dialog and also remember the last used signal
number. This makes these dialogs slightly less painful to use when testing
even though ideally we'd have a single dialog for choosing both values instead
of two consecutive modal dialogs.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65492 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775