Rationalize System Update GUI messages
Rationalize System Update GUI messages

At present, when doing a System Update, there is a message box that says:
"Please wait while the installation of completes.
This may take several minutes."

Between "of" and "completes" is the package name, which is blank in the case of a System Update.

This should fix that issue by defining $pkg_wait_txt appropriately for the $firmwareupdate case.

Note: It was also easy to refactor out a couple of special "if firmwareupdate" tests, as the code "fell out" nicely by defining the other *_txt variables to suitable strings for the $firmwareupdate case.
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