Freeze breakage: update-manager and gnome-app-install

[Sebastian Heinlein]

Dear translators,

I broke the string freeze for update-manager, since I found two strings that
haven't been marked as translatable:

"_Replace" and "_Upgrade"

Furthermore I added a new filter to provide a highly requested function in
gnome-app-install:

"Installed applications" with the tooltip "Show only applications that are
installed on your computer".

Cheers,

Sebastian

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