LT-14780 and FWNX-1186: S/R menu help

LT-14780: Users reported being confused on what update is
being checked for (Flex or Flex Bridge), so I added "FLEx Brdige"
to the S/R menus "About" and "Check for Updates".

FWNX-1186: Do a better job of disabling the two 'View Messages' menus,
when the Chorus Notes file(s) are empty.

??: Make "Check for Updates" menu not be visible for Linux,
since it has a different update mechanism than does Windows.

Change-Id: Ibb22f1f065b4ca572583496337b3734c2e1e167d