Ticket History #5612: NIM feature request - cmdline option to open GUI

The MIT Help Desk has asked if NIM could have a command line option to
open the GUI.

As discussed on the kfwdev mailing list I propose the following changes
to the existing behavior:

(1) Add --show and --hide command line options to netidmgr.exe. These
commands will cause a previously running NIM to either show or hide its
application window.

(2) When a second instance of netidmgr.exe is executed without
command-line parameters, it should trigger the default tray action in
the first instance. The default tray action is configurable by the user
to either mean "obtain new credentials" or "show/hide" the application
window. By making this change, a user that opens a shortcut to a second
instance of NIM will trigger the same action as if she clicked on the
tray icon with the first mouse button.