Improvements to Mode A/C display

Allow a greater range and negative values for Mode C (down to -1200
feet)

Stop attempting to feed ModeA/C data to SBS Output stream.

Allow Mode A only matches to Mode-S squawks when the Mode A code does
not conflict with any possible (legal) Mode C code.

Allow Mode C matches to track aircraft climbing and descending
relatively slowly. This also helps when trying to match Mode-S altitudes
which are 25 foot increments, with Mode C altitudes which are in 100
foot increments.