Short circuit limit orders with post-only set
Short circuit limit orders with post-only set

GDAX has zero order fees and a 'post-only' switch that guarantees zero order fees
for limit orders posted. This change detects the case and prevents an extra api
call to fetch the order fee.

redmeros/Lean,jameschch/Lean,AnshulYADAV007/Lean,redmeros/Lean,JKarathiya/Lean,AnshulYADAV007/Lean,kaffeebrauer/Lean,jameschch/Lean,Jay-Jay-D/LeanSTP,AnshulYADAV007/Lean,redmeros/Lean,Jay-Jay-D/LeanSTP,kaffeebrauer/Lean,StefanoRaggi/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,kaffeebrauer/Lean,QuantConnect/Lean,StefanoRaggi/Lean,QuantConnect/Lean,Jay-Jay-D/LeanSTP,kaffeebrauer/Lean,QuantConnect/Lean,AnshulYADAV007/Lean,AlexCatarino/Lean,kaffeebrauer/Lean,redmeros/Lean,jameschch/Lean,jameschch/Lean,StefanoRaggi/Lean,AlexCatarino/Lean,AlexCatarino/Lean,jameschch/Lean,JKarathiya/Lean,Jay-Jay-D/LeanSTP,JKarathiya/Lean,Jay-Jay-D/LeanSTP,StefanoRaggi/Lean,JKarathiya/Lean,QuantConnect/Lean,AnshulYADAV007/Lean