move all ufoextender range info to weapons

and stop displayed/actual values from dropping below 0.
no longer hidden options, they are now defined on a per-weapon basis.

dropoff intensity may be set

dropoff distances may be set for each fire mode

aimed shot falloff distance will be enforced for all shot types,
  IF the ufoextender range option is disabled.
  this adds an "effective max range" to weapons that will not restrict fire,
  as opposed to the maxRange which WILL.

minimum effective range will observe falloff rules for shots taken at ranges
  under the limit.