1. add gcode conflict checker
2. add a new command line option: --no_check. When it's provided, gcode
conflict check is skipped.
Change-Id: I6feafca8c5fa6c3c5eae1f0e541ce59d2f03dedf
(cherry picked from commit 5a39afb64e826a960d9673dcada89d02d62b3911)
miaoxin