VxMarkScan: polish partially configured election screen

[kshen0]

If mark-scan is partially configured by loading an election but not selecting a precinct or "All precincts" when multiple precincts are available, the election is considered unconfigured. Removing the election manager card and inserting a poll worker card will show a screen that says "Insert an election manager card to configure VxMark". The poll worker card appears to no-op to the user.

This might be confusing if an election manager has just loaded an election and believes the machine is fully configured. In this partially configured state (election exists, but no precinctSelection) we could say "Insert an election manager card to finish configuring VxMark" or "... to make a precinct selection"